If Valve started to routinely do Bad Things on Steam they'd be gone pretty quickly. Many would go to GoG, some just stop buying games. Bad Things do occasionally happen (bad things like those "oops, we don't actually have licenses for the music used in the game you bought" revokes), but Valve keeps succeeding in keeping it to a rather low background noise level. Competitors have two decades of being that good or better to catch up. You can't buy trust, you can just put money into not losing any of the trust that grew over time. When competitors have done that for two decades, Valve, unless they fail in the meantime, will have even more.