Yeah and it's fantastic that those games still exist and allow things like modding and mapping, however both of those games are a decade old. It does feel somewhat like the trend has died down significantly for newer games, no?
I certainly love them though! I'm still holding out hope for Source 2 SDK and Hammer 2 to actually become a usable tool outside of VR or Dota 2.
Facepunch [0] (Makers of Garry's Mod) are utilizing Source 2 with Valves permission and everything they're working on looks pretty promising, with great potential for a new era of modding.
Heck both of those games ARE mods of other games originally... They also both spawned off massive mods and copies themelves. Anyone remember the autochess craze of '18?
CS:GO : allows both custom maps and community servers
Dota : allows custom maps, some of which have created and radically changed existing popular games like auto chess did to Hearthstone.
These two games which are in the top 2 have more hours played than the next 8 games in that ranking.