Speaking in general, I reckon what sometimes happens is bands develop as musicians from the early days and want to showcase this in their albums. You often hear them saying it in interviews. This seems in many cases, to result in songs becoming technical magnum opuses, or concept albums. Sometimes though it's the rawness of the earlier music which attracted a lot of people to them, many of who are not accomplished musicians ourselves and don't appreciate the "improved" direction of the newer stuff. Probably this is why after a while you get a back to their roots album.
I remember that documentary a few years ago featuring Saxon where Harvey Goldsmith the PR man was trying to basically commercialise the band sound to appeal to a new audience. The band didn't like what he had planned for them and told him it was great to get new fans, but they had fans who'd been following them for nearly 30 years to consider too.
