BF:V (which btw is probably still 50$) By your logic, those games should be sold as a 5$ BF'42 mods.
Actually they are effectively now sold that way. You can get all of the BF1942 games including BF:V and the expansions for $19.99 or less total in a bundle (such as https://www.atomicpark.com/productDetail.aspx?prodId=23392 ). And both that bundle and the Medal of Honor Warchest are much better values than Red Orchestra which retails for more.
Sure the gameplay is not exactly the same but judging from the numbers of people who play and have played those games versus RO, more people prefer the other games.