Back then Netscape Enterprise Server did a bunch of stuff that Apache didn't (threads, API, certs, etc). Most people were using forking and CGI scripts, but we were saving a ton of money on colo that easily paid for the license by using NSAPI instead of Perl. Even now, over a decade later, I maintain that NES 2.01 was possibly the best web server ever written. If I could use it today, I would.
What really killed Netscape was that the only thing less reliable than NES 3 was the watchdog process they included with it to restart it when it crashed! That was around the time that Apache was catching up, and the rest is history.