Why do mods get outdated?

Either that or they add new things that are now required and the mod doesn't have them.
But most often seems like it's because the mod was just badly made and shouldn't have worked in the first place, it only worked by chance and when some bugs got fixed it broke. Then people complain and the devs have to add back things that make the mods work again, the game is full of this kind of "backwards compatibility" that fixes things that should have never even worked. Don't get me wrong, many modders know how to make mods properly (among them are most of the well-known good modders), but there are also many of those who don't. Personally when I see that something in my mod is "kinda working but just barely" I usually try to learn how to do it properly so the next update won't break it, while a lot of other people just leave that in the mod and don't bother fixing it until it's broken. Of course I'm often limited by my lack of experience so I can't fix everything, but people who don't have this problem SHOULD try to make their mods future-proof. Which is also not always possible of course because the devs may just add/change/remove something that will break some mods no matter how hard you try to avoid it.