Falcon 9 and STS do not have the same capabilities. F9 can match STS on payload but only if the booster is expended. With booster recovery F9 payload to LEO is ~25% less than STS. Falcon 9 has no capability to recover payload from space like STS [1]. They're different vehicles with different missions. We didn't need the shuttle anymore so we reallocated resources. All the F9 ISS missions are only happening because we had STS to build the ISS in the first place.

[1]: https://en.wikipedia.org/wiki/STS-51-A