Exec was designed for 128K, 7MHz, and a floppydrive. At that time OS design had included proper management of all system resources for 20-odd years already. Hi-Toro just didn't have the resources available for making it happen.
It wasn't just money, the lack of memory protection is baked into the way messages are passed between applications. Passing memory pointers between processes was a conscious decision to make it run quicker. Not only that, the mmu's available back then slowed down every memory access.
exec was still the most advanced kernel for a desktop computer or games machine in the mid 80's. None of the competition in that market were even close for many years. Unfortunately the windows/macs evolved and ate the Amiga's lunch. The Amiga was never taken seriously enough to take on Silicon Graphics or Sun, because the design fell short of the workstation market.
