It's a 3d Platformer on PC. Comparing it to other titles in the same genre:
Sonic Frontiers - 19,181
Racthet & Clank Rift Apart - 8,757
A Hat in Time - 7,312
Yooka-Laylee - 6,508
Spyro Reignited - 4,198
Crash Nsane Trilogy - 3,755
Sonic Forces - 2,058
Sonic Generations - 1,686
Crash 4 - 454 (Launched much later, originally battle.net exclusive)
Sonic Lost World - 252
Sonic Colors Ultimate - 90
What were you expecting?
Even ignoring that 3d platformers are an underperforming genre on PC compared to Consoles these numbers are still reasonable in comparison to GoW for example. GoW sold over 20m on PS4, 70k peak on Steam. Ratchet games typically sell 2-4m lifetime on PlayStation consoles, so why would it's peak be anywhere close to titles like GoW, Horizon or Spider-man.