It's because they weren't good enough for the thousands of concurrent requests of C10k or the millions that came after it with C10m. Granted, 10k concurrent re

It's because they weren't good enough for the thousands of concurrent requests of C10k or the millions that came after it with C10m. Granted, 10k concurrent requests is a problem for the 1% of websites, so processes were (and still are) good enough for the long tail of personal or small-scale websites.