Here's the conundrum I'm facing. We have two websites in the same AdSense account: first one is dedicated to food/restaurants, the second is about pretty much anything, i.e. you can't even pinpoint it to an established category, content-wise.

Both sites are years old, have sizable traffic, although at this point 'uncategorized' site is older, in decline, and has a significantly smaller traffic while 'food/restaurants' site is younger and steadily growing.

The problem: RPMs and CPCs for 'uncategorized' site are much higher in the U.S. compared to 'food/restaurants', which I find surprising. The picture is similar for other first-tier countries, but in the U.S. it's the most extreme case.

I've compared the sites using all kinds of traffic segmentation (desktop/mobile, manual ads/auto ads, web/AMP). According to these reports, the 'uncategorized' site has no significant advantage or performs slightly worse in key metrics such as CTR or Viewability, but it outperforms 'food/restaurants' in terms of RPM and CPC by quite a margin (3-4 times).
And 'food/restaurants' shows fewer ads per page, 2 vs. 2.5 on the average.

Also, I've compared the sites by 'Targeting Type', the results are as follows:
- 'food/restaurants': Personalized 69.4%, Contextual 27%, Placement 2.9%
- 'uncategorized': Personalized 72.23%, Contextual 23.2%, Placement 4.4%
As you can see, there's not much difference here, at least not enough to command such a difference in CPC.

My questions are: is food/restaurants traffic somehow discriminated against by AdSense? Have you observed something like this, perhaps in another category? Is it some kind of issue with oversupply of this kind of traffic? What CPC is considered 'normal' in the U.S. in food/restaurants category?

I do realize that content matters, but in this case it doesn't make sense to me, especially considering most of the requests served are of 'Personalized' type, which, theoretically, means that context should not play that big of a role.