You mean what exactly they're doing with Xrd, an older IP with an older audience?
I still don't understand your reasoning. At best, I can only agree with the notion of them continuing with Xrd because they invested too much of their resources in producing it.
They aren't just transforming GG into GG in 3D. I think it's more complicated than that. It's my personal opinion but here you go since you asked for an explanation.
The goal with Xrd isn't just to gather the old fanbase, it's to change well enough the game to create a new one without alienating the old fans. Arc is working with anime trends, they always did even if they say they don't take notice. When they created Guilty Gear it was during a golden era of original anime and they registered to it without even thinking about it (think Bebop, Evangelion, Trigun). When they started doing BlazBlue in 2006/2007, the anime world was influenced a lot by amateur works (dojins adapted to anime, more positive characters, school stories all the time) and they rushed inside this to make BB because Mori is probably a bit of an otaku. As a result BlazBlue is just an hyper deluxe dojin without any consistency and that's why I don't like it and why it was so successful.
There will be a time when BlazBlue will be out of fashion however, will not please any new players like GG did. Not because it's 2D, because it's out of the trend and transforming it into 3D will not change this. Tekken has the same problem with the nineties attitude of the series where electro music/colors/non-sense is the rule (bears! robotic ninjas! bruce lee! grandpa moving by doing farts!) and it won't necesseraly please a new audience. That's the reason Tekken 7 is trying something new with characters like Lucky Chloe or Shaheen while avoiding characters like Yoshimitsu or Kuma. They may come in the game later but at the moment they are not. There's a reason for that. Maybe people don't undestand what are bears and Yoshimitsu referring to?
So back to Arc. Today you're seing a lot of new anime series that appeals a lot to the first period anime fans I mentioned with more adult stories being very successful, classic themes adapted to a new generation (first that are coming to my mind are Attack on Titan, Psycho Pass, Terror in Resonance) all of them that can be watched even if you are not an anime guy. It's not quite as original/crude as before and not as amateur or "anime at school", it's an in-between, somewhere between being positive but serious. Xrd is positionning itself right inside it by smoothing his designs and characters and tone, trying to please old fans with classic designs and the promise it's as before, but also adding characters like Ramlethal, Elphelt or Leo who seems popular among new players of the series... And BlazBlue fans too from what I saw.
Simply put Xrd is not just "GG in 3D", it's GG trying to adapt to a new period where people have new expectations. GGX and GGXX, the base of all the other games, came out 13 to 15 years ago. Rebooting GG was a smart move as everyone asked for it. But they are using GG to do something else than what is what made for. As a result the game is risky as it has to find a balance.
In my opinion it didn't find that balance but that's a whole other topic.
Edit: wrote a wall of text again sorry guys. -_-