One of the most surprising things I found about this game is how few mods there are for it. It's a beloved title with millions of fans. So many other similar games which came out around the same time (Half Life, Deus Ex) have a vast array of mods available. With SS2 however the only mods out there are ones focused on graphics and sound. There's no re-balancing of Psi powers; no added weapons or abilities; no extra story content.

Is there a reason for this? Was there something about the game that made it particularly difficult to create mods for ? Were the fans just happy with the original content and didn't want to make any huge changes? I curious as it's hard to believe such a classic was left relatively untouched by the community.

pretty much right on the spot - the game is quite ok just by itself, and trying to rebalance it is a major pita (or rather, a many month job for a team of people). there were quite a few attempts, but only a handful of them actually got somewhere.

and rebalancing psi powers, good luck with that.

The editor is a pain to work with at the best of times, requiring a lot of patience to learn and make even simple changes with. I imagine this frustrated many people who tried to mod the game.

Even so, there are some great modding efforts out there. New missions, mods that try to improve the challenge, overhaul mods, etc. Rebalancing psi powers is doable if you aren't too ambitious.