Unfortunately the replacement of SOFR is a collateralized rate where as LIBOR is non-collateralized. Adoption of SOFR has been slow because its not 1:1. Plus, LIBOR is not dead yet, still a lot of contracts that need to go through maturity before the rate truly dies.
Interesting history on LIBOR, was created related to an Iran loan in the 1960s. Doesnt seem that long ago but that is pushing 50 years now. Imagine apple told you that mouse will no longer be supported on OSX, please everyone switch to touch screen -- the adoption would be slow at best.