Because most phones have enough memory to handle all the bloat, and when they don't, Google can sell those people cloud space. Not to mention that adding more memory is how phone manufacturers earn money - out of my ass example just to illustrate the concept: 100GB phone costs $400, same phone but with 200GB memory costs $500, 100GB memory chip costs $20, manufacturer pockets the difference. Having bloated apps and no SD card (iOS doesn't support SD Cards, Android makes them work like shit on purpose) justifies in the eye of the consumer the necessity of extra memory. Most people have fast internet connection so download time is always acceptably small, no matter how much bloat you put, not to mention that updates are in the background anyway.

The economic pressure to keep apps small is literally negative.