While I might be wrong could this also be some way to fight vote bots? [...] Or maybe because bots became so attractive people started buying steem dollars to pay for them?

Very insightful, but not correct I think. In fact I believe the opposite is true. People who run bots which in particular use self voting or collusive voting to up vote other bot account, they would always choose to get as much liquid rewards as they can so they can sell it quickly.

Since the SBD price is up and you can get half your post payout in liquid SBD, this has make scam bot accounts more that 500% more profitable.

This is a bad thing 😭