I've been
saying this almost as long as the game has been out. Even used the term "floor"!
I use passive checks for other skills in the games I DM. And the distinction between those and Reliable Talent (and Take 10, for that matter) is just that: it's a DM call, a tool to simply judge if I need to call for a roll, or just get a general feel for the environment. A good example would be dual surprise. Say, a PC and a monster, neither attempting to be stealthy, round a corner and run into each other. Is either surprised? In TSR D&D, I'd resolve this with surprise rolls. With 5e, I can just use passive perception vs passive stealth. If an NPC lies to a PC, I might use their passive deception vs the PC's passive insight, or roll a deception check vs the PC's passive insight, as a guide to how to role-play it. A slightly treacherous path that requires a DC 10 Dexterity (Acrobatics) check to safely navigate? PCs whose passive acrobatics clear the DC navigate it with no problem, while those who don't have to make a roll.
But if I decide a check is needed for a player initiated action, that's generally going to require a roll. The treacherous path, I might use passive acrobatics, but if the thief is swinging from the chandelier, I'll call for a roll, and in that case Reliable Talent comes into play.