The issue is not that nobody found an alternative to string theory, the problem is that nobody found a use for string theory. Essentially vast amount of funding

The issue is not that nobody found an alternative to string theory, the problem is that nobody found a use for string theory. Essentially vast amount of funding and talent has been pushed into string theory (via the tenure processes at universities which favored string theory for a long time, because it was considered the cutting edge of theoretical physics), and what did we get from it? Not one falsifiable prediction, which as Popper would tell you is necessary to do science. So everything and nothing would be an alternative to string theory.