From what I understand it's complex. Basically he got burned out from art in general starting in 2013 and got kind of bogged down doing what seemed like so many similar commissions....I.e. the Sonic TFs. You'll notice he did a lot of commissions from that genre near the end from the same guy I believe that commissioned him. That was something from what I understand burned him out very fast as it seemed too similar and he was likely getting pressured to get those done and out of the way.
After the Sally TF which was his last TF comic he just I think had it with Transformation art and the commissions he was getting. I mean you can tell something feels off on that comic compared to the others he did. Good comic but something near the end is more rushed and less polished. Again, likely was cause another Sonic commission genre for TF.
Ultimately I think he wanted to quit at that point and just stop entirely. From what I know he did eventually refund all the commissioners. He still is around. Recently in 2018 there was a very very very rough single picture from him posted from someone but people can't confirm the date which it was done and it looked very rough as if Black-Rat had taken many years off from art. He is done with public appearances on the internet under his Black-Rat name but I am sure he still floats around incognito but I think at this point life has caught up to him. I am sure he's enjoying life now away from the craziness that was art and the commissioners he was getting to do art.
He had a good run from 2001-2013 with art being one of the biggest names in the genre. Very few big name others than Loboleo are around and even he is beginning to slow down art now. Essentially the big names from the 2000s from this transformation genre have moved on or have been winding down. A lot of new artists have risen up to take the places and many many are also very talented and deserve a look.