[janderson]

Since I work for Tamiya I have some background on some of your posts. As far as why we or any manufacturer does not make every make and model of truck, there are many reasons.
Licensing
Design Cost
Tooling cost
Molding costs
(Just to name a few)

On top of that the number of pieces sold as not everyone would be interested in every model type.

And at the very top is the USA market in R/C is Ready-To-Run. The USA market would rather buy and drive than build.

These rigs are expensive enough to have RTR versions would be through the roof. Not to mention once built they are more fragile so the do not ship well and land in one piece.

Hope that helps. I do agree as a builder and such, in stead of diving in the deep end you must learn how to swim first. Build a truck and start modding it. You will learn alot from the build that will give you more insight on the hobby.