The epidemiology of COVID19 has been pretty good:
COVID-19-Related Mortality Risk in People With Severe Mental Illness: A Systematic and Critical Review
Eight in 10 deaths of people with a learning disability are COVID related
Data on Post COVID sequelae is still limited, more so a year ago when the contracts for the current vaccine stocks were being signed - it would have been unlikely to affect the judgement of UK public health officials and politicians for who a major consideration was public anxiety over 150,000 COVID deaths. What data there is on PACS suggests older age and comorbidities are risk factors so from a Public Health perspective the existing priorities achieve some coverage of possibly preventable disease as well as simple mortality.
Governments are always going to make cost/benefit decisions when they have to justify massive new spending to their electorates, and in the case of a pandemic, where vaccine supply is limited and mass coverage is impracticable year on year. Inevitably there will be gaps and inefficiencies but those charged with organising vaccinations have to guess how their particular population is going to respond.