The DM doesn’t necessarily have your modifiers memorized and asking what they are every time slows down play. The DM also likely doesn’t want to share the DC. The easiest fair solution is to always ask for a roll (assuming it’s possible, generically, to succeed or fail) and to then consider passes to be passes. If you only avoid asking for a roll when you know the player will make it, then you’re likely to be biased toward the players whose characters you’re more familiar with.

So a 1 should always be a fail.

RAW this is not the case. From the DMG:

Rolling a 20 or a 1 on an ability check or a saving throw doesn’t normally have any special effect. However, you can choose to take such an exceptional roll into account when adjudicating the outcome. It’s up to you to determine how this manifests in the game.

My experience with having nat 1s being auto fails and is that this results in characters who are “erratically … tragically incompetent” as well as taking away player agency (Nick Brown on rpg.stackechange explained this well). Maybe you and your players like a game like that, but I certainly don’t.