>>32048361it's a mixed bag of things
one one hand it was the impact of growing Youtube restrictions that hit a lot of un-seiso content hard (smacking Aki, Choco and Mel pretty hard), no dedicated gamer personality (until Pekora came to a bit more prominence), more focus on just chatting and giving viewers female attention
no one before Gen 3 really relied that much on building a parasocial relation with their audience and honestly, no one besides Lamy and maaaaybe Watame really went into it as hard since then