Post produce being too big is a factor but not the only.
Post IOI:
Pristin had 10 but they were the one that were doing good because 7 of them did well in produce with 4 reaching final and 2 debuting. Plus 1 of three not in produce did Girl Spirit. So people knew 8 of them plus they promoted pre debut with 8 members and even released "We" so fans already know the group. They failed because Pledis ditched them for still unknown reasons.
Weki meki has 8 with 4 on produce. The problem is that only Yoojung and Doyeon were known, many didn't remember Elly and Sei from produce and the other four were completely unknown. Nor they promoted much predebut with the full group. Once they debut all the attention was on the 2 from ioi and the main vocal. So here yes was a factor especially since this three are still the most promoted.
Dia is a mess, they were 7 then one was replaced, then 2 got added became 9, the other left. They were always doomed being in MBK. More than the number it the continuous line up change and the poor promotion.
WJSN were already debut and from a know company and already a big group with 12 then 13 and they are doing ok.
Gugudan were 9 and were too many. People didn't like the concept, the name, their debut being during ioi promotion. Most only wanted Semina as they had 2 amazing vocalist and a good dancer and rapper, but when the subunit was created people only cared about Sejeong as she already debuted solo. If they were maybe 5 with Hana and mimi as visual they would done better. But maybe Jellyfish would have still ditched them like Pledis with Pristin.
Chungha and Somi are doing well as solo like every member when promote alone is liked and known.
Post Wanna One:
Nuest the most successful of all but they were already debut and known.
CIX and AB6IX both from small companies and hype faded pretty fast because of long hiatus and Youngmin DUI scandal. Sad thing is that they sell less each comeback, so also the fandom in shrinking.
But i think Wanna one problem is too many solo too soon. Only Daniel is still popular both in show and with music. All are selling less with each album, with poor promotion and the attention completely faded. At least Ong and Jihoon are also actors. But no one seem to remember Jaehwan, Jisung and Sungwoon.
Post X1 is just sad. Only Victon and Cravity are doing well but aside the fandom they are not that known or talked. Drippin is already selling less each comeback. BAE173 is on hiatus and struggle to reach 20k album. Wooseok, Woodz hype have faded and Eunsang still don't have a group and as a solo is not doing well. WEI last album sold 80k but nobody seemed to talk about them after their debut. Same for Mirae but they sold only 50k.