If you want to blame anyone, blame EASA that set the increasingly stringent ATC standards and have made the UK CAA little more than a regional branch.
This is becoming a common problem across all airports in the UK, even the largest airports. ATCOs are expensive to train and employ and it takes time. Meanwhile like all skilled industries there is a retirement cliff, where experienced ATCOs are leaving in their droves having done their time and are collecting their pensions. It's not easy to become an ATCO either. Smaller/more remote airfields often have problems recruiting due to lower wages than the bigger units, less promotion prospects, the lure of working at a "prestigious" unit and perhaps most of all, many simply don't want to live in remote areas and want to stick to the big cities (bonkers IMO, so many places can offer such a better quality of live rather than living in over-polluted over-crowded holes full of overpriced houses and pants restaurant chains...)
It's becoming one of the major drivers of Remote Towers (aside from the bigger and real/more obvious reasons).