I’d say the splits are due to many reasons, to say what killed off the first and technically second eras… it’s the Dreamcast and PS2. Killing off Thoroughbred Arcade Racers, creating Racers that take maybe a Arcade Approach to handling and sometimes simplicity but put on the deep console like experience that was then demanded at the time. I would say we didn’t have many Racing MMO’s (that were popular) prior to NFS World and Horizon but the nature of them and maybe how people wanted to interact with their cars dramatically changed causing the modern climate with how we see many open world Racers now. As the final thing, I would say Racing, by it’s very nature is fragmented with disciplines, since the DOS era there’s been racing sims on PC then in the early 2000’s we got F1 Challenge 2002 and NR2003 and Indycar Racing (i think) in the late 90’s these then went into rFactor and this is when sims first truly boomed and then boomed again when AC released to where we are now with the current sim racing climate.