Because tweet never had any negative connotations before Twitter took it on. It’s the sound a bird makes. Toot is slang for farting which doesn’t have the greatest associations. It’s also like skeet for blue sky. I get why the owners wouldn’t want a word that has a whole and common on their platform community that knows that word as slang for ejaculation.

Ads are super effective. If you have something to buy, but you don’t know much about it, you will tend towards buying the thing that was advertised to you more often than not just because you are more familiar with it over other things. You might not stick with it, but being the first thing someone tries is huge.