For two reasons;
1) PoW is an inefficient use of resources that skew incentives toward miners to game the system of governance. This partly responsible for long transaction verification times and increased fees during high volume periods. It’s also contributing to the balkanization of the Internet with the high concentration of miners and mining production hardware in China.
2) Burning more fossil fuels is not a long-term solution for humanity’s energy needs.
Ok then stop using all the power in your house then. You're burning fossil fuels and that's bad.