A fairly easy answer is "one of the purposes of Sentry is running Sentry-as-a-service, at large scale". Which comes with compromises that make smaller deployments more "bloated" too, but is a very different thing than intentionally choosing to bloat it to make it hard to run.

It's definitely true that what Sentry is today, is a function of operating it at scale. Thankfully one of the intended purposes of Sentry is also that it scales down much better than today [1]. That it does not is also something that Sentry as a company is not happy with which is why there are desires to change that, which will also benefit self hosted.

[1]: this is because a) developing on sentry has become harder and harder on local machines and b) operating single-tenant installations for some customers brings many of the same challenges that people on self-hosted run into. c) we want more regions of Sentry and smaller ones (such as Europe today) have higher fixed costs than ideal.

Yes.. we're getting there. "one of the purposes of Sentry is running Sentry-as-a-service". Why? To make the dwarves happy? It's making money. And with it comes a whole truckload of very obvious incentives. Notice I don't say anyone is intentionally being evil. That's quite unnecessary.