You can look at it this way: Leisure was not that good, and if they'd kept pursuing that style they would never have been as popular as they are now. So they had to make a few pop albums (that said, this is good pop) to gain enough commercial clout to be able to afford the change.
And Parklife is a really diverse album anyway, it covers a lot of ground.
Making myself up as I go along. Check out my music-themed blog, 79:57