Maybe the main reason why there are not a lot (or any) c172 Liveries on the MS-Marketplace, is that one cannot (yet) publish FREEWARE there.
Most liveries are made by the Community and Freeware developers… most of which cannot get recognized as Marketplace Developers, and even if they did, can only sell Payware on the Marketplace, and thus pay their 30% (?) Share of sales to Microsoft.
Currently there is no FREE ride for Freeware on the marketplace.
One possible solution would be if an existing marketplace developer put together a set of existing Freeware c172 Liveries (with consent from each Livery developer), and then got them, as a set put up on the Marketplace, with a minimal payware cost.
Would take a lot of co-ordination by the Marketplace developer, so it is doubtful that it would make economic sense, especially if they were expected to share the money from any sales with each of the Freeware livery developers.