That really seems to be the basis for dramas now-a-days; let's get "good-looking people to snatch the ratings." Of course, those "good-looking" people have to be established; you can't through a good-looking, no-name individual out there to pull in the ratings.
But the thing is, most people watch idol-oriented comedy/dramas over all else (and yes, even 1 Litre could be considered an idol drama), and that includes most of Kimura's work. Usually the guys blast the JE idols, then they slobber all over the young actresses cast against them. Gender bias is what human nature is.
Japanese dramas kinda differentiate themselves in that, because they're much shorter than other Asian dramas, the supporting casts are much thinner. That in turn means the leads are asked to carry the show. In a K-drama, if you have an idol in the lead, you'll have a support system of veteran talent (and usually a seasoned costar) to kinda keep the idol afloat. (And even then, Goong S sometimes happens. ;) ) In J-dramas, the idols are often swimming by themselves.
The other thing is, J-dramas are more likely to catch teenagers to play teenagers in those lead roles. On American TV, even the WB shows were mostly acted by 20-somethings playing 16-somethings. And you could kinda tell who was the real teenager because the acting chops weren't all there yet. Those who could, you could tell would become the big stars. Yamapi is all over TV. But Takayuki Yamada is the guy I actually see constantly promoted in posters at the video store.
Outside of idol drama, though, the acting is often excellent and the people are still quite pretty. Ryoko Shinohara, Patron Queen of all Working Women, is often up there in those beauty polls. Kyoko Hasegawa and Yukie Nakama are still CM queens. Bambino features Yuki Uchida, and she's absolutely dazzling.