Might have more to do with a limited franchise with the years now ticking by before Aena has to bid to run the airport again which they might lose.
This might also explain why the council is funding the link to Parkway on behalf of the council owned LLAL as Anea would never get any investment back for the remaining years. It also puts into question about any future investment by Aena after the present upgrade is finished apart from care and maintenance.
This will always be the case, with expansion and investment being minimal while the airport continues to be run by this business model from the council.
If the council had sold the airport 15-20 years back, I would suspect the airport would be a very different airport to what it is today, and investment would have been far greater. But no point on dwelling on what never happened.
Maybe the council could sell a share in the airport like what local councils did with Birmingham Airport, but still have a controlling share. There we have seen the runway expanded, upgraded facilities for the A380, terminals merged and new terminal expansions and car parks more on par with the quality you would find at airports like LGW and LHR.