Or it's because they didn't have a record label breathing down their neck and made the kind of music they wanted to make. It was pure unrefined rock and roll akin to early Rolling Stones
I loved the first two albums. They just aren't the same band anymore and haven't been for years
Or it's because they got progressively better at playing their instruments.
The below is the first reference to it I could find from a google search, but it isn't the only one. Interviewer
: Do you think that the experience playing live helped create some of the changes between [A-ha Shake Heartbreak] and “Youth and Young Manhood?” Jared Followill
: Yeah, definitely. I think that’s all the difference just because since we recorded that’s all we’ve done is play live for a year straight basically. There was really nothing else in it. We wrote most of the core of the songs during soundchecks and stuff like that, and we just got a lot better on our instruments having played all those show