Asbo Zaprudder wrote:
The gig probably doesn't pay enough or have enough of an audience to attract Dara O'Briain or Brian Cox.
This. Plus the regularity would be annoyingly demanding on most people's schedules, especially those with other filming commitments. It would only appeal to an academic without a broader media profile, or someone approaching the latter part of their career, or somone like Brian May, who as you mentioned, who doesn't need to worry about money or another career.