I worked in NHS IT for a number of years. I've been in other industries for a while, but I doubt things have changed that much. It's not a funding or business priority issue per se. Tho having said that the NHS is focused on providing the best care to the most people. That does mean that some people fall through the cracks.

Anyway, the data is significantly more fragmented than you can ever imagine. GPs are technically (it's very odd) private companies. They can have a reasonable amount of leeway to do things as they see fit. Which means just at primary care level, there's a massive data quality issue. Then you get on to secondary care (hospitals etc) and there's just as much separation between the different trusts/health boards etc. Then each country, have their own NHS, Scotland, NI, Wales and England.

So it seems like an easy fix, but the reality is miles more complex than you might initially think.