Though I agree that the current community is in fact spread out, I cannot agree with servers being empty all the time.
If you look at the server lists, you will see that there is quite a few servers with a lot of players in them - this will always depend on the current time and the timezone.
For instance, right now it's EU time, and there are around 4-5 high pop servers in Open World, 3-4 PvP servers, 2 high popped Survival servers and two ongoing Battle Royale matches going on simultaneously and that does not include private server farmers, for instance.
There are things that we have discussed and I personally like. PvP servers should be merged with Warmup Servers and/or reduced.
These players do not sum up to a relevant percentage of the current population, we are aware, however those are players who ONLY play those servers.
Doing something like this, as you point out MAY bring these pops to a higher level, obviously. But it may also cause more people to quit playing the game because we removed the game mode they enjoy playing.
Remember these modes were added a long time ago when the general population was much higher.
It's not that simple to just 'remove' those like that, as there are loyal players to each game mode and it wouldn't be fair to them if we were to kind of 'force' them to play where WE think they should be playing.