Some of the "not so good" universities were excellent polytechnics until John Major in 1992. Delivering good vocational courses. Changed because they wanted students to have "parity" qualification wise, and also because Polytechnics were funded by the local LA and not centrally.
A lot was lost on the vocational side however, it could have been done differently. Then "metrics" begun to count, ie universities judged "by results" which again looked for academic excellence as the prime measure of a "good" university. Subjects which weren't really measurable in this way feel by the wayside even more.
Then since around 2010, and especially in the 2010s, the landscape of university metrics has become more complex and sophisticated.
This includes more nuanced measures of research impact, student outcomes, and international collaboration. Universities get funded according to things like research papers by staff and taking part in Erasmus. Again, this pushed vocational subjects further down priorities. Academics have to churn out research papers to get better funding.
Its no accident that just 2 years after abolishing polytechnics - 1994 - the self serving Russell Group of universities "Set themselves up" to try and keep what was claimed to be academic excellence but was in fact a bid by to value academic subjects above all others.
Far from the new universities being "Valued" by the switch from polytechnics, for many its been a loss. but some ex-polyechnics have centres of excellence in some subjects, by the sheer efforts of staff and management of those universities.
but for vocational training its been a lose-lose. Academic snobbery still reigns, although in terms of top level research and development/collaboration with industry it's essential to have the top end parts of further education.