Why do Bands Start to SUCK later in their career

With success, time often gets filled up with wife, kids, family etc etc. They don't have the same spare time to get deep into the creative process.

Think about it, mens motivation often are getting women and fame (so they can get women).

Then when the need is met, priorities often change. And when there is marriage and/or kids, one has to think about other people too.
Then maintenance is more important. Live on old glories etc.

Also they might invest into business in the side that takes up time etc..