I’m asking about being tightly coupled to LNBits. Your sarcasm here doesn’t even make sense to me, sorry. 

Isn’t it possible to just use regular onchain bitcoin transactions (maybe even silent payments) to buy and sell with NostrMarket? Or is the only transaction type that is supported really just Lightning?

Limiting it to lightning means that we need a whole house of cards of technology that is just really annoying to stand up and serves to keep users from adopting