Hard to make a success of the villa job, they're a side that could easily go down but have spent a shit load of money and have a few international players so would be seen as a huge failure if they did. Do well, get mid-table and it's seen as simply where they should be, zero chances of getting any higher and into Europe.
If the Liverpool job is already lined up for him and he simply has to transition I suppose keeping them up and waiting out Klopps inevitable meltdown can be seen almost as an induction, if he still has to impress to convince the candle worshippers then it'd be a poor move.