Full disclosure required I guess.
The ESS is funded by the EU
www.europeansocialsurvey.org
With results published by the well known Eurosceptic paper the Irish Times....
Ignoring the obvious potential for accusations of bias in both funding and publishing; my guess is it's probably cyclical.
A survey taken at a time when the UK was having a completely unnecessary ding dong with the EU, is bound to make people think twice - there are some who suggested that the EU positions were deliberately designed to 'punish' the UK to put other nations off leaving - in which case, they have succeeded in their primary aim.
I'm not so sure that's the true reason for a declining desire to leave the EU. I think desire for change is cyclical. High points of a desire to leave are when economies are thriving and things are going well - low points are when you feel membership shelters you from the worst of whatever is happening (this survey was done during Covid and the war in Ukraine and the EU/UK bun fight). Structural funds to net beneficiaries are quite the sweetener during times of uncertainty.
Although I don't foresee a time of EU collapse, I do wonder how long they will tolerate Hungary (in particular) mind. I expect the EU are playing the long game; expecting that Hungarians will eventually vote a different leader in and therefore may get back to being happy to be part of all the structures of the EU and not just the juicy bits which are income generators for them.