It was always their intent to remain in EASA *provided* that we could do so without having the ECtJ as the ultimate arbiter, because the whole Brexit Mendocracy was rooted in the idea than we couldn't have some grubby-little johnny foreigner having jurisdiction over anything to do with decent British folk. This was bolstered with all the blather about the ECtJ always ruling against Britain (which was utterly unfounded, but what's one more lie amongst so many). I expect they assumed that they'd be able to demand membership with our own jurisdiction, but like so many things they promised it turns out that the EU had a different view, and they held all the cards. So they then had to drop the idea of staying in EASA.
Again, the founder members of the so-called "project Fear" warned extensively and in detail both before and after the referendum, but sadly we were jeered at. So people are now lying in the bed they made.