I think City did not want to be left behind if this takes off and whilst the thought behind it that 6 premier Clubs are involved the ESL would think that the Premier League and FA and the various Countries would be reluctant to sanction all these Clubs as it would ruin their own home leagues to do just that.
However without the backing of UEFA and FIFA, who would ban players from playing in World Cups etc. you would also need to have players willing to play for the break away clubs.
In the statement it says it is not their intention to split from their home leagues merely play in an alternative European Super Cup, this coming about since they think the current format reforms are not to their liking.
Their proposals for a founding 15 teams (3 yet to stick their heads above ground, who may well include PSG , Bayern Munich and one other) and then add 5 more to the league, but this is flawed to start with because, with 15 places already guaranteed the competition in the various leagues is meaningless and prevents any further investment by rich owners into what we would call a closed shop.
I really don't think they have thought this through and I think it is there that we have a stalemate.
UEFA want to the best Clubs each year to compete in the Champions League, their new proposals have a slight compromise to the ESL, that past results mat still get you into the competition, that would not go down well with teams that finish higher in their various leagues. (eg Arsenal mid table replacing Leicester )
UEFA are somewhat at fault introducing FFP designed to stop upstart Clubs from getting on to the Top Table and once City destroyed that plan, it has all gone pair shaped and will rumble for some time.
These Clubs who have signed up to this ESL want their cake but are not willing to share.
I am sad that City are part of this but understand their reason for doing so.