Bayern had plenty of players turn over under him. Thing is when you can get a player like Lewandolski for free, then it doesn't reflect on your cheque book. Again Bayern already had strong core of players already there, so they wouldn't need to spend as heavy, something which Mourinho teams need as he more often than not went to team needing to go up the tier.
Edit: just look up and Kimmich, Alonso, Pepe Reina, Coman each cost less than 10 mil. Bayern has known to have these under market value deals prior and after Pep, so you can't use Pep or money value. It's more as Pep was lucky his spending figure wouldn't get significantly bigger being at the right clubs. Now with PL club tax, English, Homegrown player tax... he's surpassing former cheque book champion Mourinho in no time.