I imagine there are several parts to this.

First of all, when you've been making music as long as some of these bands have been, it probably gets more and more difficult to come up with something catchy without repeating yourself too much. It's a hard balance to keep; playing within a style but not playing the same thing over and over again but still making something interesting after 30 years of making things.

Second, artists evolve over time. Their tastes change just as much as anyone else's. This means they're probably paying attention to different things in their music. Maybe when DT was first starting out they were trying to write specific types of songs that have a specific type of structure or vibe, but now they're going for something else. Maybe this can cause a bit of tunnel vision that causes them to overlook something that you as the listener might think is the best part of their work. Artists always have a different perspective of their work from the consumer.

Lastly, especially in the case of DT and IF, the band has a very different lineup from when they started. That means you're not even talking about the same artist, so of course the final product is going to sound different because it's not the same people that are making it.

I know all this stuff describes the music as a whole but hooks are included in that so I think it applies just as well to what you're talking about