I'm not sure that the plans are in fact originally drawn in CAD but stand to be corrected, they do of course end up in electronic format for printing.
I agree that there are probably no technical reasons why the plans could not be included in the digital editions but there are commercial ones!
The 'free' plans subsequently find their way into the Plans Service and subsequent sales are made which help recover the original fee paid to the person who draws them.
If you mail out an electronic copy with the digital edition you are effectively giving it away to the whole world as the files will inevitably be swapped around on the internet. It isn't so easy to do this with physical plans as they have to be scanned and digitised first to recreate the file which introduces a significant hassle factor. You need to get hold of one of the original hard copies first. It may be an imperfect business model but the powers that be seem to feel it is reasonably effective in the circumstances.
Years ago complete copies of mainstream 'feature' plans were printed in the magazine because in those days the technology did not exist to easily enlarge them and it was cheaper just to buy a copy if you wanted to build the model. Now of course you can take one of those old plans, scan it in at 300dpi and bingo you have got a file you can print out at full size. But people still buy these old plans because they don't have the original magazines to copy them from and to get hold of one introduces the hassle factor again.
This is why you will only see parts of feature plans reproduced in the magazines these days to encourage people to buy copies of plans.
People complain about kit manufacturers not providing full size plans, or in the old days not providing drawings of frame sections in the old Aerokit drawings. The idea of course was to protect their copyright which is why it is actually difficult to build an Aerokit type boat from the drawings that originally came with the kit.
You don't stay in business by giving away your assets and stock in trade.
Colin