Which people did with Hybrid Theory. Then they decided to make more radio friendly songs into a compact album named Minutes to Midnight, which boosted their popularity even further because it was more appealing to the ears of the masses.
What's more important, pleasing the "hardcore" fans or making money for your career? I can see why they would choose the money route, seeing as they make only 1 cent off of every album sale as it is (on top of illegal music downloads). Pleasing a small amount of fans who want them to return to their roots is not selling out, nor is it likely to happen.
I remember back in 2001, I would ask anyone if they heard of Linkin Park before...their initial response was "Yeah! They did that song In The End, right?"
In The End was a catchy tune and more pleasing to the ears than One Step Closer.
(my point with this is that the majority of people are more likely to remember the easy listening tunes)
It's a career. It's obvious they are going to "sell out". I can't think of a single band who has not done so AND grown in popularity. When you are out playing local pubs for the sake of pleasing people, it's different than signing a contract to market your music. You can't market your music too well if the majority of your audience isn't buying the shit.
Obviously I don't have a tag on my shirt that says "Professional in Marketing" but that's just how I see it.
Edit:
Oh, I give Blackbirds a 9/10. It reminded me of Hybrid Theory, Meteora and Minutes to Midnight smashed together...I liked the vibe of it.