It isn't, that's the point of the study - not all court decisions are on wikipedia and those that are, are getting cited more. Judges, Lawyers, Clerks have access to the original decisions and court transcripts in electronic form going back decades and longer. If they're relying on whats on wikipedia - they're either doing poor research or are too lazy to write their own summations.
... and then rely on LexisNexis et al.? Unfortunately it seems that (US) courts don't really have a good collation of cases (as opposed to collated laws which exists as the US Code).
Pretending Wikipedia isn't also, is silly. This week's nonsense with the definition of 'recession' is proof enough of that. If you want to argue magnitude, you've already conceded what Wikipedia is (and I don't deny PragerU is what you claim it is).
Wikipedia is not perfectly unbiased, but if you honestly believe it is even comparable to PragerU you should seriously talk to someone about your biases and perception of the world.
There are left-wing equivalents of PragerU (ex: the Gravel Institute) that are just as far away from Wikipedia as PragerU is.
The method of this study was to deliberately construct a bias on wikipedia, which the researchers were able to successfully pull off with measurable effect.
At most, Wikipedia could be said to have a neo-liberal bias, an ideology upheld by both of the US' political parties, based on policies alone and not on each individual voter's personal and nuanced adherence. The parties are wrongly assumed to be polar opposites on the political spectrum by most US citizens, but they're not.
It isn't, that's the point of the study - not all court decisions are on wikipedia and those that are, are getting cited more. Judges, Lawyers, Clerks have access to the original decisions and court transcripts in electronic form going back decades and longer. If they're relying on whats on wikipedia - they're either doing poor research or are too lazy to write their own summations.