I used to believe that the were different groups as well and that maybe they just shared a few staff, however somewhere on this site, another proved that they are in fact the exact same team, in fact, there is a screenshot of inceston's stream page that shows other accounts they play as and RedX games was the other account, also all of their DMCA take downs includes ALL of the games from both companies, even the tax ID number is the exact same. There is no doubt, it's the same.
The reason as to WHY, is simple, people are ALOT less likely to support a Dev team that has a focus on 5 different games, because then the game you ACTUALLY want to support isn't likely to get the attention you would like for your money. HOWEVER, if you were to have only "2" games under a single name, people THINK that the title they want to support is getting ALOT more attention. They also obsessively want to add NTR into their titles and do everything they can to include NTR and NTR elements, they take more risks on RedX and can gauge how far they can push the Inceston before backlash and subscriber losses. That's why "Inceston" has an "NTR" branch and "None cannon NTR scenes" versus RedX doesn't. If you REALLY think about it, there are ALOT of good reasons to hide the fact that you are running 2 companies and 5 games.