I believe the disconnect you're having is that you aren't recognizing that an action is taking place in that example. When the player directs their character to search for a Secret entrance, their success at finding one (through whatever resolution mechanism the game uses) is what says if there is one definitively. Failure doesn't mean there wouldn't be one to find, but it does mean whoever tries again will have to succeed against a higher difficulty, and that the question of whether there is one or not has an unknowable answer until someone succeeds.
Its still a choice being made because they're attempting to avoid having to make the choice to brute force their way in, or take whatever other routes are available. To actually deny this would be robbing the players of their volition.
Now, unless the change is basically flavor, there is no reason to just unthinkingly add huge, consequential things wholesale to the world on a players whims, but there's also no reason to deny the possibility of a secret entrance to a building. That just isn't that critical of a detail and if it is you did your worldbuilding wrong.
And plus, it doesn't have to be an actual secret entrance anyway. A successful check on the players part could instead just reveal an opportunity to make their ingress easier, which is effectively what they're really asking for. The secret entrance part is not important.
Yeah, this point does get warped all out of recognizable shape pretty often in these here parts. Take Dungeon World, a typical PbtA. You can't really 'search for secret doors' as a game mechanic! You could be in a situation where you want to see if there is one, because it would be logical and useful to you. So, certainly a player could state "I check these walls for cracks, markings, or anything else that seems indicative of the existence of a secret door.
Now, this isn't exactly one of the 'moves' that the player has, it isn't a standard move, nor a playbook move. So, the GM could reason "well, no move is triggered here, its now up to me to make a GM move, being guided by the principles and mindful of the agenda." Said move could be "You do notice some oddities in one section, and the nearby torch bracket seems a bit cockeyed." OK, so the GM has framed something into the scene, and typically it will lead to more 'adventure'. The GM could also simply decide some orcs come along while you are dawdling, or whatever.
Another consideration here in this sort of play is that things kind of depend on context. If the party is urgently attempting to give some people the slip, then maybe Defy Danger produces the result of a secret door by which to do so. This one will need a check, the character's might end up better off or worse off. If the player describes their search a bit more generally, it could also be considered to trigger Discern Realities, and the player will ask the GM one of a list of pretty general questions about the area. Assuming a secret door has high utility, and the roll was good, the GM will not be OBLIGED to describe a secret door, but they will need to give the player something useful, so it might be a pretty solid obvious move.
And, finally, note that narrative consistency is a basic assumption. If it is already established in play beyond a doubt that no secret door exists, well, why are you searching? It won't suddenly show up! The GM is required to honor existing fiction. It would probably be bad form for the GM to put a secret door in a ridiculous spot too. That being said, there's a lot of stuff in the world that seems pretty illogical at first glance, but the world is complex, old, and filled with odd stuff! I expect a fantasy world will be too. Going along with that, the GM is supposed to emphasize the fantastic in their framing. In fact GM prep COULD put a secret door there, in which case I'd imagine the PCs would find it for sure if they look.