PSOE-C would require a huge 180 on behalf of Rivera. Which he could do because he's done it before, but after his present campaign it would be even more difficult. And he himself seems much more of a right-winger than he liked to admit, though he's showing more of his true colors now.
I think Rivera has made a strategic mistake by aligning himself to the right to such an extent, which weakens both the combined right and C's by causing PSOE-C swing voters who don't necessarily appreciate PP (let alone Vox) to move to the PSOE. Might as well just shut up about your coalition preferences, win more votes, join a right-wing coalition (or even lead it), and have these voters leave you for PSOE afterwards while you're in government anyway.
They pretty mcuh no choice, they did that move when all the voters who supported for their hardline about Catalans moved to Vox/PP and they fell in polls to nearly 10%.
It was a choice between either confirming their new selling point or giving up on it and searching a new one (but an electoral campaign isn't the time to do that).
