Most people that are currently mining XMR are doing so at a loss (electricity costs exceed revenue). The only logical explanation on what they do with the XMR they mine is that they hold the XMR, in expectations that it will increase in value.
I can say this because I'm a miner also.
Bolded an important word. There are definitely miners who either do not pay for electricity or are using other's.
Yes, of course There are also miners utilizing optimized software to get a much better hashrate than their competition (us). And there are miners out there that also pay extremely little for electricity. But it all comes down to the fact that mining XMR is less profitable than mining WhirlpoolX or X11. So of course, they are either holding the XMR or they are dumb and dumping the XMR while they could be mining on NiceHash and making 35-55% more.