Why people build in caves? Because you have more space, it's 10 times easier to defend, it requires less resources and you don't have to worry about your breeders and babies getting sniped.
Fixing that will be hard because of all the changes Wildcard has made to the game. Let's look at turret limit, before turret limit you could build bases big enough to safely store all your dinos. People didn't build in caves as much back then not only because of no turret limit, but also because of the maximum turrets you could fit on a turret wall, what I mean by that is, for most caves you couldn't fit more than 200-300 turrets on a death wall, which compared to heavies damage wise is approximately 50, let's not even talk about tek turrets, they received such a big buff back then and now, since patch 295.102 (Use FastTurretTargeting system automatically for anything moving faster than 300 cm/s) it's impossible to run a turret wall if a server isn't lagging really bad.
One of the only reason people built in caves back then is because you could AFK on a giga with autoclicker at the crouch spot, making it almost impossible to do anything.
Also let's look at extinction, it's only made everything worse. Even though cryopods were added to reduce dino storage issues, tribes are now mutation breeding with insane amounts of 0/0 cloned females because of how much element you get from extinction. Extinction not only added that, but it also added velos which strengthen cave defenses by a lot, meks, titans, snow owls and gachas. Why would people ever build a land base when meks titans snow owls and tek tapes are a thing, your best chance to kill a titan is to cryo a giga or velo on top of it. If all 3 titans manage to download your turret tower/base just gets rushed by them, backed up by paracers meks tek tapes and gigas.
Literally all you need outside of a cave is a teleporter for meat and berries. You don't even have to do boss fights anymore, people running gachas 24/7 is more element than you'll ever need.
The only real counter to caves right now is the tek railgun and it's not even close to enough.
So my suggestions are:
1. Change cave entrances, make them larger and remove all crouch spots. Maybe add multiple entrances.
2. Add a different turret&structure cap for caves, for example make it so you can't place more than 100 turrets in the entire cave.
3. Change north ice cave's artifact of the clever side, the drop point is too op, and there is too much space behind it.
4. Revert changes made to turrets in patch 295.102
5. Change the way mutation breeding works, maybe add an actual mutation cap.
6. Add a tek saddle limit per alliance.
7. Add a mek limit per alliance. Nerf mek shield radius.
8. Nerf titans and their special abilities(forest grab range, ice breath range&freeze time)
9. Disable placing hatchframes and chairs, benches, toilets on platform saddles.
10. Drastically increase turret limit/decrease its range. Make it so turrets over the limit actually don't work. Change it to alliance limit.
11. Do something about meshbiting.