The biggest 6 clubs in England have enjoyed lax financial rules to beat out competition in England (also in Spain and Italy) and therefore should be rewarded by creating/controlling a competition which will create even greater inequality?
Barcelona want it because they're worried about debt; Juve want it because they're worried about Atalanta over-taking them; Spurs want it because they're good with money but bad with football; Arsenal want it because they're at risk of becoming a mid-table side....
Owners of these clubs want to:
i) restrict competition to reduce the risk of a Leicester City like season
ii) prevent financial risk of sustained bad decisions
iii) create even greater wealth for themselves
iv) break from current fanbase and responsibility to local area
It's an extreme version of what they currently have and what is being suggested by UEFA - neither of these are great and have several issues.