Pressure from everyone to get something shipped and out-the-door - never-mind the technical debt - and after it ships management is only interested in further growth fuelled by more features - deepening the technical debt.
As for the problem of Apache keeling over too easily - that’s because Apache (at the time - and I think still now) is based on “one thread per HTTP request” - or one thread per connection. Asynchronous (or rather: coroutine-based) request handling was very esoteric in the late-1990s and early-2000s - and required fundamentally different program architecture - no-one was going to rewrite their CGI programs to do that - and Perl script based applications couldn’t do anything at all. Asynchronous HTTP request handling only really became mainstream when NodeJS started getting popular about 7-8 years ago - but, to my knowledge, besides ASP.NET Core - no other web application platform treats asynchronous request handling as a first-class feature.