Generally, gear doesn’t break unless something explicitly says so.
Sunder explicitly involves attacking equipment. Various spells also explicitly mention damaging equipment. Firearms can misfire, as explicitly described under their rules. Equipment with the Fragile property also have an explicit chance of breaking.
But without such explicit mentions, gear just remains, unaffected by whatever’s going on. Your character is assumed to be keeping care of his or her gear in the background, the same way he or she is assumed to be training in whatever skills and features he or she will be getting at the next level-up, as well as more mundane things like hygiene and bathroom breaks. It’s not that these things can’t be brought up to the foreground – roleplaying training or upkeep can be fun, give the characters a chance to interact in a more calm setting than typical. Issues like hygiene or meals that often get elided and assumed can become important when something prevents them from happening. But if the players do not explicitly go roleplay these activities, they are generally still assumed to be happening. There’s just a time-skip for the sake of keeping the game moving.
This is a part of Pathfinder’s abstraction level
All games, by definition, require abstraction, since we’re not capable of simulating real life. When, where, and how much abstraction to use is an important part of a game’s design. For Pathfinder, and Dungeons and Dragons 3.x before it, this abstraction did not include wear and tear, random equipment damage, or explicit upkeep rules.
The reasons why are multudinous, but the primary point is that the designers weren’t designing a game that focused on these things, weren’t targeting an audience that was interested in these things, and so designed the game to skip over them, allowing it to better focus on “more important” matters (from the view of their design goals for this particular game).
Unfortunately, for D&D/Pathfinder, the abstraction level I refer to is not particularly consistent. Some things are more abstract than you’d expect considering their prominence – the battlegrid and HP are two major examples – and other things are bizarrely detailed and simulation-y despite not at all being the game’s focus – the “dragon flight simulator” rules come to mind. As a result of this, and the frequency with which D&D/Pathfinder have disconnects between how things are described and the things the rules actually back up, it’s easy to get the impression that D&D/Pathfinder are much more exactingly simulationist than they actually are, and that the systems are capable of supporting a much greater variety of gameplay styles than they actually can do justice. D&D/Pathfinder are not particularly generalist systems, they are devoted fairly tightly to, well, delving dungeons and slaying dragons, the stuff of heroic fantasy. The farther away you step from that paradigm, the less well-suited the systems are going to be, and sooner or later, it’s just not going to work out well at all.
Changing this now would be very difficult to do in a consistent and fair way. The whens and whys of real-life objects breaking are complex, and the exact construction of the item matters a great deal. Moreover, from a gameplay perspective, some classes are far more item-dependent than others, so this change hurts them more than it does others. Unfortunately, those same classes are also already the weakest. So I do not recommend attempting to add in rules for this sort of thing. To do it justice would be difficult, and you’d either have to change much of the game around this modification, or have inconsistent and (more) imbalanced mechanics.
Instead, if this is important to you, I would suggest that D&D-derived games, at the very least the Wizards of the Coast editions, aren’t well-suited to your desires, and other systems might do a better job matching what you’re looking for. Like I said, D&D et al. are designed for a very particular game, and there are plenty of games that they just do not do particularly well. And there definitely are systems designed with this kind of thing in mind.