It's true for both big and small development studios to a certain extent; smaller developers often are more open to sharing ideas and discussion of their art projects and book venues to disseminate news and get feedback about their game in this manner, rather than curated theatrics to sell product. It's not bad to want to show and announce a product when you feel it is ready, but my argument is that the industry is cultivating a culture where their audience is entitled to a project announcement curated and distributed solely in the way a company wants it to be announced, and if the message is off-brand, PR has swayed public opinion to be upset and frustrated by "spoiling" a product announcement.
I'm using product announcement judiciously in this context because when the argument shifts towards marketing optics, analytics, and theatrics of a preview, it's not artistic, it's utilitarian.
I can understand why a businessman would be upset that their product announcement leaked. The audience upheaval, the unadulterated anger and disappointment over a leak, is not productive or healthy. And I think this audience frustration is in part due to constant bombardment of marketing and PR jargon that has seeped into our culture from corporate framing of narratives.
I think i understand your overall point, but how would you see it being handled differently? Should the consumers be entitled to the opposite, like deciding how a game should be revealed and such? If so, what would the reasoning behind that be, and how should this be handled? Or shouldnt the developers and publishers say anything if they're disappointed that their game announcement got leaked? If yes, why shouldnt they do that if they want it?
How is utilitarian being defined by the way? Its true that trailers are made to make a product look interesting in the best way possible, so you can call that being utilitarian in that sense, indeed, but why would that be a bad thing? As long as they dont lie about something in the trailer, i cant see why that would be bad. People might not be a fan of CGI-trailers or something, but its not claimed to be gameplay or anything like that, so its not propaganda at all. Same thing with when smaller developers show of their game in the ways you mention, that is also to make the game better, and also so that it can sell better. I see nothing wrong with that. And this doesnt take away from anything being art. An artist who paint can still paint and make art, but still want to sell the art as well for example. That doesnt mean that the person isnt an artist as well. And what would the opposite be in this case if it shouldnt be utilitarian? How would you personally go about to change this? Its not like the developers want to make a trailer that makes the game look less appealing :)
When it comes to these leaks a few days before the official announcement, i dont think it has much to do with be off-brand or anything like that, but maybe you're thinking more in general? But these leaks basically just confirms the title of the games and that they exist, not much else is mentioned. The main thing these leaks hurt (as far as i can see) is that the people working on the announcement dont get the same excitement of announcing something completely fresh since other beat them to the punch by leaking it. I dont think that this is really damaging to the game overall when it comes to its commercial success in the long run. Or have anyone who works in the gaming industry said that there other reasons why they dont want these leaks to happen?
You mention businessman in specific, but can you understand the same feeling/point of view from a developer as well?
Personally, i dont think that this has much to do with the bombarment of PR and such. Thats not the reason why i'm sometimes looking forward to the press conferences at least. I think its simply a case where people are being somewhat disappointed that an event that they were looking forward to might not turn out to be as exciting as they've initially hoped for. The press conferences is a form of entertainment in themself, afterall. There isnt anything unhealthy about that, and i dont think people should be criticized for feeling this way (maybe that isnt the intention, but it could be interpreted a bit like that, in my opinion). Its not like game announcements in general is a rare thing outside of E3, so i dont think people "must" have the announcement through events like E3 to be happy with a game being announced. It can come down to personal preferences, simply what people like a prefer.
Another thing is regarding how the press conferences are being done. I remember when Nintendo announced that they werent going to do live shows anymore (at least for the time being), but rather do a pre-recorded session instead (Nintendo Direct). Some people prefer the live show instead of this and were (intially at least) disappointed by Nintendo doing this. Its just a matter of preference, and i think the way how games are announced also falls into that category. That said, there hundreds, if not thousands of people giving their opinion on this however, so naturally i cant say for sure how everyone feels about it, but in general, i dont think people put that much into it. Maybe it looks more like that because things are in written form.
EDIT: And just to add my view. I sometimes prefer announcements at events like E3 because i then know that i have something specific to look forward to. If i know "everything" in advance of the event, then its not as exciting to watch it. I'd still watch it most likely, but it wont be exactly the same. Its just how i feel, its not because some gaming companies have taught me to feel this way. At the end of the day though, this wont affect my enjoyment of the game itself :) So its not that big of a deal to me. It doesnt really matter that much to me how it was announced.