Shift from EU to US
Clegg was brought in to help Meta avoid sanctions and controls (responsibility) from the EU. He knew how the EU functioned and had a high enough profile to ensure nothing ever stuck to Meta.
Now, times have changed. EU isn't the primary threat of change, it's a president who owns and runs a direct social media competitor, who's main ally also runs a social media company.
They need to keep enough Republicans on-side to ensure that doesn't happen. And Clegg can't achieve that.