I just partially agree on this.
There are already maps released that's qualitiy can compete with the out of the box maps imho.
Have some patience and more features will eventually be implemented. Right now the focus is naturally on fixing bugs and increasing the experience of the main campaign. This game seems to be even more successful as Larian was expecting, and if they see GM Mode players are present and keep asking for features I am pretty optimistic they will see the long term potential of this and keep improving the GM Mode. Let us be patient.
Having a longer life spawn of that game including niche players who mainly purchase the game for its GM Mode feature does not mean "Zero profit in return"
For a flourishing modding community I do see the cultural significance of free mods.
On the other side i remember buying two addons of NWN2 mainly for the assets. Never played the campaigns. So personally I totally would like to have an Asset, Map, Feature DLC (maybe even some cooperation with WotC !!)