Lin it is because they are finally at the stage of botanic research where they can do DNA research on plant material the same way they do on people, and place plants in categories where they belong if they are not already there. When we were out at Tom Wood's, he was talking about having provided some DNA samples for a plant discovered in the wild that had been placed into a genus, and after testing it was determined to belong in another genus. So it was moved over. There have been several Anthuriums that have been moved from one group to a different group based on recent DNA testing. That is what has happened with these 'philodendrons'. Their genetic make up has been shown to be Thaumatophyllum, not Philodendron. There are a ton of Thaumatophyllum hybrids being made now by collectors. It should be an exciting time if some of these new varieties come to market.
