The reason you see bits in the bitcoin-core gui is my fault, it was the first PR I ever did to bitcoin in 2017. I was quite the bits maxi back in the day. Its still a great system to think in if you still like to compare to fiat. When 1 btc = 1 million fiat, then 1 bit is $1, and 1 sat is 1 cent. These days i increasingly find myself thinking in sats and msats for accounting, but i still like bits.