I think it is because hot toys and sideshow did a 1/6th from the classics so they thought fans wanted something else.
For example, hot toys has no plans to do r2 or c3 (for now) because they specifically mentioned sideshow done one and they thought it was great.
It is more about two companies trying to cover a large SW character base.
Overall, still a bit confused at the few people who don't mind this vader though they hate/dislike the movie it came from. Vader isn't Vader. For me it's like why first edition books are different to any type edition book (for book lovers) or a wine from the same vineyard but different year (for wine lovers) or same car but different year etc (for car lovers). Must be the degree of "hate/dislike" towards those movies. Some like the movie, some don't!