Very hard for resin casters to be viable. There have been a few that have been successful but a majority find that just don't make enough money to make it work. Resin casting is low volume. One is doing real well to get 50 copies before the molds break down and need to be replaced.
The original parts parts were a failure because of economics. A typical kit was $2. The parts packs were I think like 69 cents or more. To build a model from parts packs required 5 packs. A body, frame, suspension,engine , tires. It all added up to be a losing proposition.
Where as a single kit has only one.