well considering that Tony figured out time travel in half an hour after finishing the dinner dishes, theres really no reason why Thanos couldnt figure out that all he needs is a mobius strip tooTrue. It wasn't explained well. One could argue that being a super alien warlord allowed him to study the substance use his advanced tech and probable army of techs to engineer more. That would be my first guess. I don't know what the in cannon reason is though.