When I was young I studied physics. The initial idea of string theory is kind of cute. It kind of answers the question what the quantum version is of a rubber band. But that does not really work out as a fundamental theory because it has to live in 24 dimensions, contains tachyons, and there are no fermions. To fix this people invented the fermionic string. Already at that point this seems a somewhat artificial thing to do. The thing is that ever since the question was posed it is still quite unclear how to bring general relativity and quantum field theory together. String theory was interesting for so long, I think, because it complicated enough to contains lots of interesting mathematics but not complicated enough to be completely intractable.