alt Hacker NewsIt is running on a single machine so the player count is relatively low. Today the limit is ~1500 concurrent players but it used to be much lower. And of the players online probably half are bots which don't build.
The map is 30Mx30M blocks so outside of the very center you'll not see that much player activity.
DonutSMP is the largest Minecraft server today, the overworld is 225,000x225,000 blocks and the map is modified wherever you look.
And because destroying other's builds is allowed most of the impressive builds are hidden in the middle of nowhere. Building within 50k blocks of spawn comes with the expectation that it might quickly turn into a crater or lava cast