that experts aren't rating many lagers at all in the upper tiers of the rating level. I would think that a beer should be rated on its own standings, sure, but also within the context of the style of beer it is. There should be some bocks or pilsners or Märzen style beers receiving high ratings for being exemplary offerings in those styles.
Even with the good bocks, märzen and pilsners there aren't may more than a couple handful of good lagers and with the incredible oversimplification of the categories in that chart I very much doubt whether märzen or bocks were even counted as lagers at all (I'm guessing no).
The difference in ratings can also be explained at least partially from how the drink is consumed. Heineken is pretty ok, if tasteless, from the bottle but pour it into a glass and the fact that you can smell it properly will make it much easier to detect it's flaws.
I think what happens with many people (certainly myself) when they start branching out from their AALs is that you go see what the highest rated brews are so you can try some of the best stuff out there. Almost invariably, this means a bunch of super strong ales. So over time, you find that the higher-rated brews by experts are these strong brews, while some of the lighter lagers and ales are lower rated, influencing your own opinions towards "stronger flavor = better beer".
I started out chasing the highly rated beers as well but if you take a good look it's pretty obvious how hype is a huge part in the top ratings, now I only check ratings to see if an expensive beer I want to buy isn't rated really low as I don't want to waste my money. There is also a large difference in what people are looking for, I greatly enjoy the cheap lager I usually get but it's by no means a great or even good tasting beer, it's just unremarkable in every way, unoffensive in every way and I can drink a few without thought.
For me personally there's a big difference between drinking "a beer" and drinking a craft beer and rating sites are aimed at the latter, the ratings are based on depth of flavour, aroma and the finer things in beer and "a beer" doesn't do well in any of those.
I'm sure there's also some taste fatigue, where there will be lots of beers out there that are very similar in taste, so you're looking for something that stands out from those
This is actually something I think about quite a bit, in the Netherlands almost all breweries start by making the classic Abbey style ales (blonde, double, triple) while in the same stores and even supermarkets you can get trappists for the same or a lower price. It's something I just don't understand because your Quad is lovely but it's more expensive than the Rochefort 10 and St Bernardus 12 in the same store while it's nowhere near the quality, why would you set yourself up in a direct competition with beers you're not going to beat in price or quality? Especially when almost none of these new beers offer anything new, it just boggles my mind.