It's not that I personally find it hard.

It's more like, a lot of stuff in Wikipedia articles is somewhat "general" knowledge in a given field, where it's not always exactly obvious how to cite it, because it's not something any specific person gets credit for "inventing". Like, if there's a particular theorem then sure you cite who came up with it, or the main graduate-level textbook it's taught in. But often it's just a particular technique or fact that just kind of "exists" in tons of places but there's no obvious single place to cite it from.

So it actually takes some work to find a good reference. Like you say, review articles can be a good source, survey articles or books. But it can take a surprising amount of effort to track down a place that actually says the exact thing. I literally just last week was helping a professor (leader in their field!) try to find a citation during peer review for their paper for an "obvious fact" in the field, that was in their introduction section. It was actually really challenging, like trying to produce a citation for "the sky is blue".

I remember, years ago, creating a Wikipedia article for a particular type of food in a particular country. You can buy it at literally every supermarket there. How the heck do you cite the food and facts about it? It just... is. Like... websites for manufacturers of the food aren't really citations. But nobody's describing the food in academic survey articles either. You're not going to link to Allrecipes. What do you do? It's not always obvious.