As a Google engineer, I believe it is largely accurate to say that we "don't care", or at least "not caring" is the emergent behavior at Google. There are many things we don't care about at Google that I think would shock many engineers who have a healthy amount of pride in craftsmanship. It's hard for me to precisely describe why we "don't care", but I will try anyways.

As the parent commenter has pointed out, pulling in client code can be very large. If the backend team owns the client code, they may not be properly incentivized to improve the product of the clients, sadly. And calling it the backend "team" might be overly simplistic. There may be additional layers to the the client code owned by other teams, such as different protocol implementation and definitions of those protocols, etc. Pushing for change can be viewed negatively, since it could leave a poor impression. E.g. if you improve someone else's code, that could make them look bad, and that would have negative consequences for you as you have violated (a variation of) Greene's first law of power: never outshine the master.

Since the code and the organization are so convoluted and complicated, it's a lose-lose proposition. If you mess up your optimization, you will get blamed. Even if you succeed, you may have reduced someone's reputation of someone you can't even identify in the bureaucracy, and thus have made an enemy of someone you can't even identify.

I think a simpler explanation the some of the others is.. why care? Phones these days, even cheaper ones, have oodles of GB available. They're not losing customers from the size. And I don't think making it smaller is going to draw in new gmail/workspace customers. So why spend time on it when there are tons of new features or active bugs that could be fixed instead?