I don't get it. Why would anybody in their right mind want to heat a building using the waste heat from electrical devices when it's far more energy efficient to just use a heat pump?

Well the heat is going to be generated from high capacity computer processing so might as well capture it and use it because you can't mine cryptos with a heat pump

Would it be profitable for people to invest in a mining op if I started one because my electricity bill is the same every month no matter how much electricity I use.
What part of the world are you in? I pay the same every month but December. That is when I have to settle my account. Either they owe me a credit or I owe them extra.
I live in the US, my job gives me housing and I pay a certain amount each month no matter how much electricity, heat, water, or anything I use.
Start a big PHS Mining Operation then. Get a couple of thousand Antminer S3s