why is bitcoin considered programmable money?
and how is it different from ethereum?
This page is the answer :) Ethereum is more advanced in contracts,its touring-complete,... however ethereum is mess, it is very hard to orientate yourself in the code. So the code could be very bugged (and there is high possibility that it actually is). That's why bitcoin is much simpler which makes it better.
You can create scripts and options what you can do with scripts will be improved in the future.
Ethereum uses smart contracts. Bitcoin is a lot simpler - it just uses blocks from the "block"-chain, that's where the name comes from. Look at mempool.space and you'll see all of the incoming transactions for bitcoin. It's considered programmable money because you can basically do whatever you want with it unlike fiat (like usd) which requires a lot of red tape.