Isn't it because of cuts from central Government which has been halved since 2010?
IIRC something like 25% cut in central funding, whilst also seeing a lot of stuff transferred over to them that used to be funded directly.
People also tend to see the headlines when somethng has gone wrong, not when it's gone right and forget that several things have really hammered long term projects started before about 2018, including covid, energy prices and so on, most of which are totally out of the control of the council.
They also forget that IIRC a lot of the materials needed for construction went up a lot more than anyone expected, far higher than any realistic project had allowed for in their contingency funding, which combined with the other factors tends to mean that there are a very large number of projects private and public that went well past their original budgies.
IIRC there was also at least one of the really big construction/project management companies that the councils used that went bust, just to add to the cost overruns and delays.