Change the way the pick/ban system works for regular season only (not playoffs) to force more diversity in the maps played.
Only have 3 map options in the pick/ban for every match. Home gets 1 ban, visitor gets 1 ban and the 3rd map is played. This way the league can rotate the maps week by week and still give the teams some flexibility on choices.
Week1 - Pick/Ban Maps are -- Metalworks, Gully, Granary
Week2 - Pick/Ban Maps are -- Snake, Sunshine, Process
Week3 - Pick/Ban Maps are -- Viaduct, Clearcut, Bagel
Week4 - Pick/Ban Maps are -- Propaganda, Reckoner, Badlands
If the league can agree on a larger map pool you can easily have the right amount of maps for an 8 week rotation, meaning you can evenly space the maps out for the entire season.