Regional Landmarks (Payware) Add-Ons?

I'm wondering why we don't have more landmark add-ons for larger regions or even better countries. I'm only aware of ORBX Great Britain Central landmarks. Churches, mosques and other religous buildings, power plants, stadiums, castles, etc.. are still missing in many regions. Of course, it would only make sense for already published SimUpdates when those (missing) elements would be added on a big style. Living in Germany/Austria, where every small village has a church and many castles are around, such an add-on would massively improve the visual experience. I know there are many freeware landmarks add-ons available, one chuch here, one castle there and a power plant elsewhere, but it is very fragmentary. Why not professionally combine them in a larger package and bring it to market? Is it such a big effort to produce it, or do developers don't see enough possible sellings?

For me, such a payware add-on for France, Switzerland, Germany, UK or Austria would be a no-brainer. What are your thoughts?