Because people were angry or disillusioned and had turned on his party or abstained, I don't see that as an inevitable consequence for all of these MPs, some yes, but not necessarily all. Some could benefit from gaining votes for the same reason the LDs lost them and they should keep their personal votes.
I'm not saying they'll all keep their seats, far from it. But it's not foregone that many could, given the current climate.
The way I see it they have 5 potential pools of voters.
Personal votes.
Centrist Labour voters.
Centrist Tory voters.
Disaffected Lib Dem voters.
Hard Remainers.
Just the first 2 (depending on party defected from) could be enough to keep them in a seat. It will keep Coffey in imo.
Then there's further permutations in some constituencies, Soubry being a prime example, where she had a very small winning margin thanks to a mass migration of voters from UKIP to Labour.
By standing on a Remain platform, she could lose a lot of votes and yet increase her winning margin by pushing those voters back to UKIP or over to Farage's new party while decreasing both Labour and Tory voter numbers.
It's not as simple as people like to paint it.