It was a convenient thing for Putin to have a layer of plausible deniability. It’s Wagner committing atrocities, not him. And how much money is the Russian military spending in a place like Syria? They aren’t, they’re making secret payments to Wagner. How many casualties in the conflict there? It’s not Russian casualties, it’s Wagner casualties.
In Ukraine Putin got desperate and started to rely on Wagner more and more. And allowed Wagner to grow it’s ranks and become bigger and more powerful. Another big miscalculation for Putin.
So TL;DR, Putin relied on Wagner too much because he was desperate.
patchymoose