pirates. Steam is just one distributor though, there are alot others.
Also not every of the 120 mio Pcs is as strong as an Ps4 and can run games like Witcher 3 and co. Some are laptops, low budget or old pcs which are only able to play older games.
and? what is your point in the end? even if we include all that (steam not the only sources, "PIRATEN" not every pc capable) the userbase should still be higher for pc.
so in this case it really is a reverse userbase?
I doubt the userbase will be higher.
Assuming 50% of all steam registerd pcs are laptops, old, slow. so your 125 Mio are just 62,5 pcs that are powerfull enough.
Easily every 2nd pc onwer pirates (because its easy on pc, many gamers are young and dont have money and its pretty safe). So your at ~30 Mio. Thats already smaller then the Ps4 userbase.