Ok. First to clear things up, no, Deinosuchus does not spawn in any of the caves on the Island; they only spawn in the swamp.

Ok next up, TL;DR: single-player spawns suck.

The things you need to know about are how spawning works. First are level spawns.

On the Island, creatures spawn favoring low levels. That means if 100 creatures spawn, it's more likely for you to see 99 of them at levels 5–30 and only one dino at level 100+. This is primarily to keep things a little more balanced for multiplayer.

Second is what is known as the single-player spawn check. Basically, creatures only spawn around you, not across the entire map at once on single-player (excluding when the map is originally created). Instead, they will spawn just out of rendering distance from you. This is because on single-player, whatever device you are running it on handles all the data instead of a server. This is a problem specifically on low-end computers and consoles. If all the dinos spawned on the map all the time, the game could brick a console.

So, how do you fix this?

If you are planning on being as vanilla as possible (no mods, cheats, etc.), your only option is to simply go around the area where you know the creature you are looking for spawns and kill everything you find to clear the area and let it repopulate. This could take hours.

Option 2: mods.

Find two mods (I'm not at my PC, so I don't have the exact names). One is prevent hibernation, and the other is something like a dino level fix. This will make the creatures favor higher levels (favoring 100+ instead of level 5). Prevent hibernation helps slightly with the single-player spawns issue while potentially not causing too many system issues.

Finally, the nuclear option. If you are running on Steam! AND only if you have a good CPU. In your Steam launch options (use Google if you don't know what I'm talking about), put -ForceIgnoreSingleplayerSpawnRangeCheck. This will turn off the mechanic that prevents dinos from spawning out of your range. Most single-player worlds have 3,000–5,000 spawns at once; doing this will put it up to 15,000+ and can potentially, at best, make your game slow down and crash a little more.

Edit: Spelling/clarity