I think this idea comes from the top (in other words, the CEO) and his brief is obviously to maximise income and reduce expenditure.
They are moving (and have been for a few years) towards one centralised CAA so a single number for contact where you have to hold like you do for BT or any one of the high street banks seems inevitable. They are a regulator and, as an organisation, have no reason to offer any level of customer service. At least they haven’t moved to an Indian call centre like BT and even Pratt and Whitney.
I have been dealing with the LAA recently and, to be honest, the CAA are a little better than the LAA when it comes to delays and for the same reasons, too few staff with knowledge.
Where that leaves the regulation of UK Aviation with Brexit is anyone’s guess. The CAA has been on a diet to meet it’s lean and mean role under EASA. It will take years to replace the skills lost from the CAA if Brexit means leaving EASA also so I would expect worse is yet to come at the CAA.