Getting something like AOM would have been easy back in 1993 because the costs would have been much lower. Back then complexity had to be really low, which means most of the complicated modern tools were off the table. Coming up with something equivalent to MPEG-1 would have required just a handful of engineers over maybe a year. In terms of IPR, there would also have been much less to check than today. OTOH, the minefield was moving really fast at the time, which could have added some complications. In the end, I think the main reason nobody bothered with something AOM-like is that few people realized the huge problem of patents on standards.