How is bit coin mining profitable for guys in their house?

The only people making money from mining bitcoin are people who started mining 2009-2012 and build a facility for themselves and bitmain. Bitmain basically controls most of the mining power of almost every coins that is worth something aka bitcoin ethereum litecoin, etc. Also, besides that, they're selling hardware for mining that's kinda overpriced unless you live in Iceland and have access to free unlimited electricity. Probably the people you've seen mining arent mining bitcoin because it's almost impossible (99.99%) to profit running it in your home as electricity will f*ck you over. Some coins that you can actually mine without expensive hardware are monero, eth and some others that are kinda small but may become profitable in the long run. But as always, crypto is completely speculation so thinking about a long-term thing may not be the smartest thing to do.

pd: dont fall into "cloud" mining sites as almost all of them are scams and some (eobot) let's you mine XRP which is not mineable (they're using your power to mine whatever coin they want and pay you almost nothing compared to what you could've made alone.