Lol...I literally have run into countless deer and even punched them in my play through. I have no idea how you haven't seen more.

Procedural generated maps can produce funky environments. In my map there are areas that seem to be animal deserts and other spots that wear out your weapons quickly. The comment about the respawn triggers for wildlife are another variable.

The "world" is immense, and diverse

you most run arround the meadows , boars and deers spawn in each 64mx64m

Just run around exploring more. I generally get enough by running around and marking large mushroom, and rasp/blue berry spots. The boar lore stones almost always have pigs around them unless you revisit them too soon. You can breed pigs if you want to by feeding them plants, but it is generally easier to just hunt them down.

I found a small starter island works really well. The game seems to want to provide a certain number but if you are in a small space they constantly respawn in a timely manner.

Too large an area can really seem to spread them out making them harder to find.

it is these types of difficulties that really make the game more interesting to me. Each map presents unique challenges to overcome.

Mob spawn seems to be randomly assigned to points on the map on generation and how often this respawn happens depends on some factor like how many player structures are affecting their spawns...

Try this, build a ton of workbenches all around the outer perimeter of the meadows and have a smaller area in the center that is a wide field that has no player buildings. Then you end up with say mobs spawning in said area because they can't spawn elsewhere.

In further regions away from the center of the map, mobs spawns more often, and especially when you have two biomes with mobs killing each other, resetting the mob count.

Meadow+Swamp creates a situation where at night undeads outright goes around murdering all the animals and chases them around.