It's more like hedging their bets. The Chinese proposals (CEPC + SppC) are simultaneously underwhelming in terms of performance specs and over-ambitious in term

It's more like hedging their bets. The Chinese proposals (CEPC + SppC) are simultaneously underwhelming in terms of performance specs and over-ambitious in terms of timescale. There's also always a chance that they will never materialise. If they do actually get built, construction of the FCC will be cancelled and CERN will participate in (and hopefully improve) CEPC+SppC. Similarly if Japan builds the ILC, FCC-ee will be cancelled and CERN will join that while bringing forward the FCC-hh.