Where does the money come from to pay back he loan and get your collateral back.

I mean that depends on your specific financial situation.

• Maybe it comes from your job (that you automatically pay taxes on).
• Maybe it comes from from a different loan (refinancing).
• Maybe it comes from a bag that recently became long-term capital gains.
• Maybe it comes from a bag that's actually in the red and can be used for tax farming losses.

So you tell me where it comes from.
If the debt you owe is $50k and the collateral on that debt is worth $200k or $300k it's not that hard to get the collateral back. Unfortunately this is a new contract and there is no vault control... otherwise you'd be able to pay back the loan with the underlying collateral itself... or just leave it locked and extract even more money from the position. Very much hoping they add this type of functionality in the future.

If it's a zero percent loan and you can make 20% interest on HBD why isn't everyone just doing that?

Nobody wants to hold stable-coins in a bull market.
Honestly that's not a bad plan but it requires BTC/ETH collateral... not like we can just do it directly with Hive (yet).