Steve Baker is to Comservatism what Corbyn was to Labour, he’ll play brilliantly with the hardcore contingent within the Conservative Party, but he’s not going to attract swing voters.
I’m not sure them picking anyone from the current cabinet would help them either TBH, they’re all far too tarnished by the way they’ve shown zero integrity and enabled and supported Johnson in undermining our institutions and the checks and balances of power.
To restore any trust, they need to select one of the MPs who have shown a bit of backbone and integrity throughout Boris’s reign. Tom Tugendhat or somebody of that ilk. I don’t think Brexiteer/Remainer matters any longer, we’ve left, and no Conservative MP is going to make rejoining the EU a Conservative Party policy.
Baker is also in severe danger of losing his seat: he'd have to jump to a safe seat if he wanted to become leader.
It's not rejoining the EU that's the issue, I agree that no politician is going to support that (for the moment, at least) but there is the question of our future relationship with Europe. For example, rejoining the Single Market or the CU - that's what many inside the Tory party membership are worried about.