In the early days people were blocking off large chunks of the planets, such as a wall, ceiling and floor around gems and rare resources - so they essentially had those gem spawns to themselves.
Then there are unintentional cases where people place their builds near or on rare resource spawn points, essentially delaying respawns due to activity in the area.
The most malicious cases, but thankfully rare, are the people who just plot the resources so that nobody can have them - themselves included.
I unfortunately don’t see an immediate solution to this. The developers could step in and assess on a case by case basis, but as popularity grows this method becomes harder and harder to enforce. It isn’t really a long term solution. My only suggestion would be to increase the number of exo planet spawns.