In additional support of the achievement feature.
From the developer standpoint, how much people is playing your game do actually matter; its not just about the single copy sold, but how much memorable as developer you are. Overwatch's success came from people remembering Blizzard, Apex Legend from undercover love people had for the team of the unfortunate Titanfall.
With AAA grade games given for free each year, the average gamer already own a quite big library (of often never played games): the time people will spent with your game is getting scarce as each day. On console things old up because each new generation force a "library reset": by library reset I mean when the gamer got their shiny new hardware but the true potential comes only with absolutely/from day one games (every new PC has potential to run all the library as brand new generation).
Even if you sell copies, be memorable is what really pushes you back: even your customer will forget to be your customer at all!
Achievements were made for this exact propose: make your game more memorable outside the gaming time. Completionist takes extra time to play your game even they are fed up with some slight flaws. After a gamer abandon your game for long period, when they return back they are freshly meet with their former experience (past experience find easy link through memory).