I know enough people have already said it, but the whole "you're licensing not buying" has been a thing for as long as I've used Steam.
The answer to your question though, for me anyhow, is convenience. It is very easy to buy games on Steam, there are frequently sales where you can get games for lower prices. It's super easy to play your games with a friend using Steam's in-game overlay, and it also gives a unified platform where you can show off achievements, clips from your gameplay, screenshots, share guides about games, browse forums about your games, etc.
On top of that, Steam has become a trusted name for many people, myself included. While they can take your games, legally speaking, they don't- and they're very often pro-consumer in a way that many other companies aren't. (To address your Destiny example, Destiny is the one that decided to sunset half their fuckin' games it was one of many reasons I stopped playing. Didn't matter where you bought it from, you gotta connect to Destiny's servers to play at the end of the day.)
On the contrary, they've done many things that are helpful to gamers- and yes they also help Valve/Steam, but comparing to others in their field, it's worth noting imo. Steam pushed VR adoption ahead significantly with their Index headset. They've done phenomonal work in making gaming on Linux viable without extra work from game devs, which is especially great with how Windows keeps getting worse and worse. Up until recently, if you had a legal dispute with them, while it WAS subject to arbitrition, they would pay all legal costs, whether you win or lose. (that has since changed after a law firm took advantage of that to try to pin Valve with hundreds of individual claims in order to get a payout, but I digress).
I've got my issues with them- being a TF2 player, I'm still sore over their treatment of the TF2 bot crisis and their overall neglect for their older titles. They need to get their shit together for moderation purposes, the amount of bot accounts and scams are downright shameful, especially with how obvious it is once you know the patterns. But overall, when compared to their competitors such as Epic (for game distribution) or Ubisoft, Activision, etc (for game development), they're one of the better companies imo.
I remember doing a playtest a few months back! I'm really looking forward to when the full game releases. c: