Because the guns still feel the best in this one.Neither of them will work anymore. If they want to continue down the GaaS model its gotta be microtransactions for cosmetics. Why would I pay monthly or a large sum every few months when there are options in the market that provide me content for free.
Personally I play this game enough that I save all kinds of money not buying other things, so I'd like them to keep the current model but charge more for the annual pass so they can do story content - and less repetitive quests - as well. But I know most people would rebel at that idea.