There are a lot of different things that would have played into them discontinuing the Fusion Plug-ins. The largest one is cost. Back when you could get the plug-ins they only came with the Pro versions which meant you paid an extra $100 or so. Part of what the old owners did was put a lot of "Content Creation" features into the Pro version. The problem with that is that a user may have wanted to use the Fitting Room, but didn't care about the plug-ins. So they either did without or paid $100 more to use a feature. Poser 12 gives you all the features at a lower price point. So everyone can convert content from say V4 to La Femme.

All the software's involved are being updated all the time, and not at the same time. So it takes a lot of programmer time to keep everything up to date. So the Question becomes, How much are you willing to pay for those plug-ins? The old method to spread the cost was to keep "Pro" features out of the Basic program which leads to people either buying a more expense version and pay for a lot of what they will never will never use, or have a program where they are dependent on someone making what they want. It also lead to an issue where Pro Poser could use Gamma Correction and make content that the Basic Poser could not use. So that leads to useless program bloat. Gamma Correction is a very vital component in getting proper renders. .

ETA that Poser is expecting people to use FBX to transfer between programs. If it doesn't work write up a ticket.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13