Keeping in mind that the selection of fun maps will expand in the future. People won't be keen to stick to one map only and then needing to purchase additional maps again.
An alternative suggestion would be to give Settlers, Colonist and Founders "Storage Slots" where they can pick 1, 2 and 3 amount of maps monthly out of 6 available maps (total fun maps: 17 currently) in addition to the Free Map. If not monthly, it's possible to switch to bi-weekly.
Having the options to access everything reduces the value of these fun maps. It goes against the concept of Less being more / Paradox of choice. Hence the proposal above about only offering 6 maps to choose from.
Settlers: Free Map + Selection of 1 Map
Colonist: Free Map + Selection of 2 Maps
Founder: Free Map + Selection of 3 Maps