I think they would have signed on as part of their deal for Discovery. My opinion is they are keeping a Pike series quiet so as not to overshadow Discovery season 2. I think all along one of the main purposes of Discovery Season 2 is to set up a Pike series. If this is the case, it would also mean the Enterprise bridge was built using the Pike series budget and not the Discovery series budget.
I am not so sure, with what happened last season I think it would have been understandable for them to wait to see how the new characters and Enterprise are received before they throw money at it.
I doubt they have a budget in place for Pike/Enterprise yet so it would be the Discovery budget that is used which makes it even more telling that they did not just redress another set instead.
Any series that has the Enterprise in it will inevitably overshadow Discovery I do not think that can be avoided, perhaps CBS have decided to separate Enterprise from the Discovery show earlier than intended so they can move the timetable forward, we just do not know for sure.
We may never know what the original intentions were for the series both before the changes were made in season one and the two writers were sacked in season two.
Perhaps the decision was made to shorten Discovery run but go all in and setup a big lead in to an Enterprise show.
As for the actors all we can say is that Mount and Romjjin-Stamos were contracted for one season only, any work they do on a new show would require a new contract and negotiation which may already have been done to ensure they are locked in and cant be taken elsewhere.
For all we know CBS does not and never did have any intention to have an Pike/Enterprise show and intend to go in a completely different direction.
Two aspects make me doubt the above though.
1. Suspicious that we have not heard about Pecks contract, knowing his status would be a dead giveaway at this point.
2. No movement yet on the Georgiou/S31 show or Picard, I would have thought they would be full steam ahead by now if they want to have a Star Trek show on CBS all year round, I think they may be holding off to make space for Pike/Enterprise instead.
Whether or not that was always the plan remains to be seen.
They only really built the bridge set and elevator. The rest of the ship (corridors, ready room) was just the Dsicovery sets redressed. That is entirely within DIS' budget.
In fact, I really think this is intended as a "backdoor pilot" (like "assignement:Earth" was back in the day).
Like, they were playing with the idea of a Cpt. Pike series, probably had contracts with the actors in place, but still wiggle room to let it go, if, say, people didn't respond to the ideas.
Now if they do want to make the series, they'd have to built a LOT more assets - in fact, I think they will also built new corridors and stuff. And probably have to pay more for the actors. But they already have the core idea covered and presented, onstead of relying on a piece of paper to show their producers. And if it doesn't work out - they would have really only "built" one bridge set. They did that before (the Shenzhou bridge, which they redressed for the Section 31 ship, and the Klingon "Sarcophagus" bridge, which became the Mirror Universe throne room and later the Klingon Senate). They could redress that for future seasons for whatever they liked as well. It's only one intricate set.
But my guess is, at this point, we'll get a Cpt. Pike/Enterprise series, replacing DIS as the "prequel" series. A Cpt. Picard series in the "present". Put DIS somewhere in the future (either concurrent with Cpt. Picard - or do that stupid "fall of the Federation" concept in the far future - or even turn it into Doctor Who). And squeeze the Section 31 show somewhere in there (concurrent with Cpt. Pike) as well.