Here's something that always bothered me about Samus' armor…
If it was designed by the Chozo and they're extinct, why does it always change in appearance, sometimes drastically (as in the case of Fusion or Dread)? And how does it form around Samus' body? Has Metroid lore ever covered that? Also I think it'd be dope if, for the new suit, Samus had to defeat certain EMMI's and download their information into her suit for any upgrades to work. Maybe you could also upload virus packages into other EMMI's to expose weaknesses on how to defeat them.
Not going to touch on Fusion and Dread, since there are legitimate lore reasons for her suit changing appearance in those. The intro to Fusion explains everything you need to know about why she looks so different.
The Varia Suit changes appearance repeatedly, because devs just don't care about consistency, and wanna re-design something that already works. It's supposed to be the same Varia Suit, so it really shouldn't be changing in appearance very much, but again: devs don't care, they just wanna do their own thing (with the exception of Retro Studios, which I'll touch on in a moment).
Here's Samus's Varia Suit in Metroid 2:
Then Super:
Pretty consistent, right? Clearly the exact same suit.
Then, let's take a look at her Varia Suit in Prime:
Again: very consistent. It's essentially just the classic designs, re-interpreted for a 3D space. The proportions are a bit less bulky, and there are a couple added features and alterations, here and there, but you can tell it's still the same 'ol Varia Suit.
Next, Prime 2 & 3's:
They've made further changes, altering the shape of the visor, among other things. I think Prime 2 and 3 are peak Varia Suit. Faithful to the design from Metroid 2, yet also different in subtle ways.
This is the point where the various artists and designers across a couple different dev teams start to think they can meaningfully improve upon / make major changes to the classic design.
Other M's Varia Suit.
What happened to any detail in the design? Various visual features have been eliminated, only to be replaced by generic lines everywhere.
What happened to the shoulders? Why do they now need to be so perfectly round, all of the sudden? What happened to the ridges of the older designs?
What happened to the arm cannon? It's been smoothed-out, and now resembles a toy, more than a weapon.
Why is the suit so shiny now, all of the sudden? It makes Samus look like a cheap action figure.
Yeah... I consider the Other M Varia Suit to be a low point, for sure.
Moving on to Samus Returns.
I don't think I need to tell you the ways in which this really isn't anything faithful to the original Metroid 2 design.
The shoulders have now become comically oversized beyond reason.
There are bright, glowing, showy green lights all over the place, whereas in previous designs (Retro's), they were more subtle, and well-incorporated.
The visor has been made to appear slimmer, and it really doesn't even look like a visor anymore, it's just a bright, glowing Y shape. You can't even see her eyes behind it, even though you absolutely could in previous games. It suggests less that there's a human behind the armor, and more that Samus is just a robot, or something. The exhaust ports on the shoulders contribute to that perception, as well.
Much like in Other M, Samus still looks like a cheap, shiny, spray-painted action figure, too.
Sorry for the large post, but yeah... the more recent Varia Suits are not good, in my eyes, and at points, they don't even appear to try to suggest that this is the same suit, the same character. Going back to your original question: the suit looks different because the devs decide they want to mix things up, and the end result isn't always great, sadly.
