Mr Johnson could not cope without him, or perhaps Mr Cummings knows something that would cause embarrassment. Mr Johnson has been willing to sack cabinet members, so I cannot think it is cowardice.
Mr Johnson's inactions in February and March have led to many more deaths than should have occurred. If the Tories had chosen Jeremy Hunt or Michael Gove, there would have been fewer deaths and a better functioning government. Neither would have had 3,000 people coming from the hotspot of Covid 19 Madrid to a large gathering (football match), for example.
Cutting off journalists asking questions about this shows yet another example of how Mr Johnson seeks to evade scrutiny.