Our friends at Tough Pigs received this statement from The Muppets Studio:
The role of Kermit the Frog is an iconic one that is beloved by fans and we take our responsibility to protect the integrity of that character very seriously. We raised concerns about Steve’s repeated unacceptable business conduct over a period of many years and he consistently failed to address the feedback. The decision to part ways was a difficult one which was made in consultation with the Henson family and has their full support.
That support from the Henson family seems to be confirmed with this Facebook post from Cheryl Henson: