Some issues that string theory has:

- We have not found any evidence for it.

- Some predictions have been made from it that weren't found (e.g. no supersymmetric particles in the LHC).

- It can be tuned to fit almost fit any universe and any observation, which doesn't really make it scientific.

- The reasons for inventing it might have been misguided or flawed. (universe must be beautiful / simple / etc).

The lack of results are turning a growing part of the scientific community off, while there is still a core amount of scientists holding on to it.