Speaking personally... it's because I as the DM have probably not yet determined whether the action was or wasn't succeedable in the first place. It wouldn't be until after the rolls were made and I saw what happened with the dice that I'd go with it and made it "true". So whether I ask them to make a roll or they offer to make a roll doesn't really matter, as the roll usually will occur regardless in order to figure out what the truth of the scene actually is.I still submit, as I did upthread, that this specific example is perfectly achievable with the player not asking to make a roll. The player describes what he or she wants to do. The DM considers it and asks for a roll, using a contest for some reason to come up with a DC. The player succeeds. The outcome in this case was the same. But from the player's perspective, why would I want to roll in that situation? I'd rather my action just succeed. The meaningful consequence that followed my failure on that roll might not have been good.
This is most definitely a style of DMing that I know many other people DO NOT go along with... the idea that things just "become real" in the moment an idea is made and a die roll confirms it. I've read enough posts here on the boards to know that that is an anathema to many DMs. It's part and parcel to the "Players help shape the narrative" concept that many DMs disagree with, and the whole "it's never okay to fudge die rolls" question always reaffirms that.
So I understand why you and others wouldn't go along with the idea. But at least you can see why other people might. Because every single one of us DMs differently and there's no "right way" to do it.