Originally Posted by river
It remains because mainstream science is more established and has more money
No, it remains mainstream, because nothing as yet has invalidated any part of GR including BHs, and any potential new theory, so far has not been able to "run the gauntlet " and stand up to proper scientific scrutiny.
Oh there has been theories , such as Cosmic Plasmas , that have challenged the mainstream thinking but they get no time , funds etc.
Nor respect
Perhaps there will come a day when a University is funded with state of the art observational equipment and labs and journals dedicated to sound alternative theories