What would you then consider to be a “reliable source of information”? It sounds like your criteria for that are so high that it’s unlikely anything would reach up to that level. After all, should we ever trust any source as “the ultimate source of facts”? If all you wanted to point out was that noone can absolutely trust all of Wikipedia then fine I guess, but I would hope and doubt almost anyone here would have that mindset.
I would also say that many Wiki pages have a mix of overall neutral or positive-leaning text about the subject while e.g. a criticism section includes very good negative-leaning info. As an example, the Disney page (https://en.m.wikipedia.org/wiki/The_Walt_Disney_Company) has mostly neutral or positive information about the company, no doubt much of which is written by Disney fans. But it also has a good and sometimes savage criticism and controversies section. I have of course seen Wiki articles that are very skewed, but I’ve also seen very skewed research articles, lexicon entries etc. Wikipedia’s rules and the community of moderators trying to apply them as best as they can gives it a better chance than many other sources to correct in time at least.
Another point is that less and less counts as “the most generic of things”. The basic facts of biological development, evolution, even meteorology and chemistry are being increasingly questioned with nonsense. There is an immense value in all the hard work poured into improving, spreading and preserving that “generic” information. Wikipedia is a collective treasure shared with all the world. It shouldn’t be taken as gospel, nothing should like you point out, but despite its imperfections it’s worth so, so much.
Of course, there are different opinions, but here’s my take (as a Swede, but not an expert in politics/history):
The issues didn’t start during the last decade. In the 90’s, it was politically decided that schools wouldn’t be nearly as centrally managed by the state as they had been, instead municipalities would handle most school-related politics and administration locally. It was also decided that parents are allowed to choose more freely where to send their kids. This weakened public schools. Moreover, legislation was introduced (in the 00’s I think but I’m not sure) that allows for-profit private schools, which historically AFAIK had been prohibited.
Parents usually don’t have to pay anything extra to send their kids to private schools, and for each private school pupil more tax money flows into the private instead of public schools. The private schools are of course incentivized to attract children from families that are well off, since they tend to perform better (boosting the school’s score and thus reputation), have parents that can e.g. drive them from a longer distance, and just generally have less issues and so cost and complain less. For instance, it’s been reported that some private schools refuse (openly or through loopholes) e.g. special needs pupils since the tax money paid to the school for them isn’t worth the cost (and “bad PR”, no doubt) of actually giving them a proper education.
Sweden has also had a high rate of immigration the last decades. Immigrant parents understandably tend to not be as savvy about the school system and have less time/resources for getting their kids to “nicer” schools further away. Immigrant kids also tend to require more attention, both due to needing to learn Swedish and because psychological problems, e.g PTSD, are more common among many immigrant groups. Also I haven’t seen any studies on this, but IMO the private schools’ advertisements (on billboards etc) tend to be very geared towards “white” kids/parents with no immigrant background.
In 2007 a tax benefit for “homework help” among other things was introduced, halving the price parents have to pay for private tutors at home. This again benefits families that are well off and lets private companies in education siphon tax money.
All this means a cycle of segregation seen in so many countries. Public schools are burdened with students that require more resources, while private schools do everything they can to snatch up low-maintenance pupils. This makes private schools seem to perform better and gives public schools bad reputations. Racism and class discrimination also plays into all this of course.
It also doesn’t help that teachers’ salaries and social standing have decreased, partly due to the same general patterns.
This degradation of the public school system has continued during both left-wing and right-wing governments, though it’s often accelerated during right-wing governance. For instance, the social democrats party was the one to push in the 90’s for shifting responsibilities from the state to municipalities. There is an ever growing issue with corruption across the political spectrum (but worst/most blatant on the right), where it’s become quite common for politicians to push for decisions that benefit private companies, then retiring from politics and joining said companies’ boards etc.