It was the intention of the government right up until April last year to remain in EASA and this position was supported by the CAA and industry. This position on EASA remained for nearly a year through the Johnson premiership and after Johnson appointed Shapps as Transport Sec. It wasn't until April last year that Shapps let slip that the UK would leave EASA. So why the sudden change in position when it was OK for Johnson and Shapps prior to this point? I think it is purely down to the snap election victory giving Johnson and his masters in the ERG the green light to do whatever they wanted no matter what the damage under the cover of more "will of the people". Full throttle ideological hard Brexit.
Because they have become very clever at running government through focus groups and Twitter, Shapps has never actually been put on the spot and explain his decisions. All we have had is a corny line from a DfT spokeswoman - remaining in EASA is not compatible with the UK having genuine economic and political independence. Which means Baker, Mogg, Francois etc just cannot bear the ECJ being involved in anything and as a result, we will all have to suffer.
The great Brexit irony is that we now have to comply with far more EU laws than we did when we were in the EU.