At least for systems/rulesets - PF2 in my case - having a community of enthusiasts code and enter data leads to faster turnaround times and maybe even better product quality (less strain on single authors). Their main motivation is "I want to play that, too" and some "this is something I am proud of producing". Of course both system/rulesets and content preparation are not free, but these volunteering enthusiast pay for end-users in time and effort. Some offer Patrons, like the author of PdfToFoundry (which I became a member of) and some explicitly don't want money (like the PF2 folks).
And a group of people deciding on both priorities and interpretation of rules (for automation) eases the situation of the whole system userbase being dependent on the goodwill of a single person, like with those FG rulesets that are maintained by a single person.
I use 23 extensions on FG and 88 modules on Foundry (some of which are shared libraries), with many of those being features I want/like, not necessarily what is needed to play. The PF2 system needs less addons than other systems and tends to "eat" the most important ones for better compatibility and support. 6 of my Foundry modules are updated to use features of the next major Foundry update. 3 modules are "outdated" for the current version already, but after testing all my modules I find these to still be working (v.8.9, v9 might be different).
Knowing that Foundry is still v0.x software and innovating left and right I am not too bothered by the whole modules situation yet.

