What causes different/variable ETH payout when having stable hashrates?

Hello everyone,

I'm still kinda new to mining and stuff, but there's something that's not clear for me.

I have a steady 319MH/s but in week 1 I'm earning like 0.1 ETH and in week 2 like 0.12 ETH. First this was very stable but now, in the changing crypto markets, it's very unstable.

What causes that variableness? I watched a YouTube video the other day and this guy was saying something like: "when money is going out or in", but that just confuses me. Can someone explain this to me? And maybe some examples?

​

Thanks in advance!