of the dozen or so players I know well 3/4 of us own PHB and at least 1 other book... about 1/3 to 1/2 have tasha's too... there is no adventure (not one) that we own more then 2 copies of between us except curse of strahd, and I own 2 of those.
On the other hand there is no 'splat' that none of us own... but there are adventures none of us own (one of the early dragon ones, and decent, and the heist one none of us own.
now not as well I have known others that DO own those...so it's not like I think they didn't sell... but compared to PHB and MM and DMG, I would bet the BEST selling books are less then 1/2 the sales... and some are most likelt 1/10 the sales.