The gap between rich and 'poor' teams has become too big... a perfect example how money ruined this game. Small teams have literally no chance anymore, aside from a verrrry few exceptions like atalanta maybe.
money gap was always there, we had always 2 good and 2 bad teams in ucl groups. sometimes you have napoli-bvb-arsenal group but thats usually one from 8.
i think its more about teams/names that qualified to ucl, and at top of it lacking the spectators creating additional pressure/atmosphere. imagine:
atalanta <> milan
ferencv?ros <> celtic/rangers
krasnodar <> cska/spartak
rennes <> lyon
başakşehir <> galatasaray/besiktas
Midtjylland <> aek athens/olympiacos
kick one of above teams and add benfica or sporting
also many teams are in crisis/need rebuild (real, barca), many 'top teams' dont really play interesting football (psg, mu, chelsea) or dont have interestnig players to watch.