This question has been asked so many times, and it's so obvious what the answer is. SRB2 started development WAAAY back in 1998. And 1999 is when they actually started using the doom engine. This game is still being worked on after over 10 YEARS. This game is made by fans, in their free time. After SRB2 is finished, I can guarantee that most of the devs will want to move on. If a SRB3 would EVER be made, I bet anything that it wouldn't be made by STJR.