Jose was public about where his immediate priorities lay. Eriksen along with Toby and Dire was what he wanted. (Eriksen was obviously determined to make his move but he strutted around like a peacock when both Dier and Toby signed. (FWIW I think Dier is OK and I was glad he signed a new deal with us, I also think in a "normal" team, that's to say one that plays a bit of football rather than spends most of the game spend with our backs to the wall that people wouldn't be chucking rocks at him. But I was all for Toby to leave, who has been brilliant for us but was completly clear he was on a big decline).
The point is had Jose let Toby leave and sold Dier he would have freed up £225k in salary that could go towards paying the salaries of new CB's. I don't know what we would have got for Dier, the market is somewhat fucked, but I'd guess it would have been in the region of what it would have cost to bring in Skriniar. If he didn't want Sanchez he could have sold or loaned him out, he didn't, there was zero discussion about him leaving, so one can assume he was and has been in his plans.
He didn't rate Foyth, probably hasn't seen anything of CCV so went with advice to keep him on out on loan).
That's how building a squad works and the manager builds his squad from the pieces he has and from those he doesn't want.
We have 8 players on our first-team books that can play CB (Toby, Dier, Sanchez, Foyth, Tanganga, Davies, Rondon & CCV), there are loads of options for Jose to take, he could sell all of these if he wanted to. It is his job, he's the manager.