Don't understand people who are very well read, but still not very good readers

I'm not thinking of anyone in particular as I write this: it's just a stray thought I had awhile back. Have you ever noticed how there'll be people out there who read tons of book--they read constantly--but they still seem to be kind of undiscriminating? Like, they'll praise stuff that's bad and be turned off by stuff that's good? I don't get it. This s…