The current ESEA pick/ban map system is terrible for new maps. My team banned cardinal every-time both seasons because none of us wanted to take the time to learn it when we could just ban it. I scrimmed the map one time per season because the other team had to play a match on it. How many teams played a single match on granary or badlands the entire season? Even viaduct, teams decide that they'll ban it in the preseason and then never play it.
In terms of the maps themselves, why try working so hard on pro versions of maps like badlands and granary when there are maps and mappers willing to work hard on better maps. Granary has tons of flat areas, a nightmare for scouts, a terrible mid for medics, and has the still unfixed door clipping above. Dagger is also a less experienced mapper, and it shows in some of the differences in lighting and the terrible forward spawns on mid. The main flaw of badlands is the spire, which makes a great MGE arena but is terribly impractical. These aspects of the map are super core to their design and basically unfixable. Yet inspiration from these maps exist, with the large crates on process having a distinct granary mid feel, many maps having spires or half-spires on second, and several newer maps having badlands or granary style lasts.
When it comes to testing new maps, the competitive TF2 community shows itself, again, to be strongly in favor of the status quo. Remember when there was serious talk of a pro mod for TF2 after the sticky nerf? And all the complaints about pryo being more viable (some legitimate, some less so)? When people pug, they want to have fun and get better at the same things over and over again. New map pugs could mean practicing something which will never make it to the league, could have serious flaws, and means players can't follow the same routines on the same maps which are already ingrained in their heads. Re-framing this as being pioneers and innovating all the newest strategies and mastering new maps before anyone else has even had a chance to play them could be a powerful motivator. Exploring the new is a valid way for people to have fun, and exercise some of their understanding what is the best way to play TF2, rather than just memorizing the way to play the most popular maps.
But this is all based on the existing paradigm of competitive TF2. Valve has expressed some interested in some new paradigms. Years ago Valve talked about how they would like to have a change in the competitive TF2 meta every six months or so around the scope of the old highlander black box meta change. This doesn't really jive with the current competitive community's vision for the game, but perhaps a fair amount of changes in the map rotation could serve a similar purpose, and make Valve think about the competitive TF2 community a bit differently.
In terms of what to actually do, I'll list some things from least extreme to most extreme.
1. Revert to the old weekly map rotation system. Perhaps delay the exact order until the just before the season starts to keep from having to play one map for 4 weeks straight.
2. Pug new maps often. After you've pugged it, talk about it a bit and have someone make a post in the map's thread.
3. Have 2 newer maps in the league rotation. One brand new, one which was brand new the season before. This means that there's a serious chance for new maps to become staples, with the second season letting people better figure out a map, and play without its flaws. I hated metalworks its first season, but by its second season I liked it, changes were made after league play and I got to see it back again, better than ever.
4. This is probably an unpopular idea, but more varied game modes. Valve wants all the classes to be viable. Pubbers want to be able to watch their favorite class see a fair amount of play. Valve wants competitive and casual to be closer to each other. Payload has the perpetual problem of the cart bitch, but A/D CP could work well. A map designed with competitive in mind could allow for quicker round of stopwatch to a best of 5 (to Mason's point). More A/D and koth maps could mean more varied class play, enticing both Valve and pubbers. Imagine if about a third of the map with A/D, 5cp, and koth each, that would certainly be more varied. PLR and CTF blow in competitive, but has anyone even tried pugging PD? I haven't tried tapline, but that's another possibility for more variation.
The biggest problem with all of this is that the competitive TF2 community is still around in a 10 year old game because they like it the way it is. This kind of change is unappealing to that aspect of the community.