[account42]

> Of course there are reasons, otherwise people/companies won't do it, and users won't use bloated browser that give them no benefits.

The reason is of course control. Things running in the browser gives Google control. That's why they push for everything running there. Want to compete with Google? Tough luck, no tracking for you while they give themselves IDs built into the browser. Do something Google doesn't like? Maybe your site isn't "safe" enough according to Google and won't be shown to users. Invested in your webapp but want to integrate something novel? Guess who gets to decide if you can?