Yeah there have been some different views on why these were produced over the years, was it just after hours fun with a view to sell to collectors interested in stuff like that or were they somehow linked to the POTF2 line or other concepts? The general consensus is that they were produced for the collector market but who knows..
They are almost like official customs..made from the same moulds that produced the original hard copies + 2 Ups at Kenner yet made some time after the originals were. They tend to be picked up by people interested in pre-prod that can't source or fund a true hard copy or want one as a stand in for a run (say someone has a first shot and a sculpt but no hard copy..a BH piece allows them to fill the gap if the original hard copy isn't available or didn't survive).
Very interesting pieces that's for sure, I've been looking for a reasonably priced 8D8 2-Up for years now, there are about 4 out there but even though they aren't true pre-production items the owners aren't parting with them..so that says a lot about how interesting certain collectors find them.