Well -- first thing is lets decouple your premise. You imply that all the technology you listed was designed with server side in mind. It wasn't: C#, Ruby and Java are general purpose languages not targeted at the server explicitly.
Second, if you don't think C++ gets complex (and has entirely different working models based on who is writing it) -- I recommend you use it more. C++ is a damn complex, deep, feature packed language. C++ server side frameworks exist (and are the fastest thing around: http://www.techempower.com/benchmarks/) but they take massive amounts of effort versus some of the newer languages.
PHP took off because of shared hosting, wordpress and pragmatism. People who were inexperienced could (1) get access to it, (2) deploy it and (3) get things done.
ASP.net survives (most would argue it didn't really take off) because if you live in the MS toolchain, it is a very nice experience.
I'm not sure about ASP.NET - projects I've worked with are utterly over-engineered with so many interfaces, services, factories, and service factories, that it's impossible to figure out where the code is that actually does anything, even in VS2012.
Second, if you don't think C++ gets complex (and has entirely different working models based on who is writing it) -- I recommend you use it more. C++ is a damn complex, deep, feature packed language. C++ server side frameworks exist (and are the fastest thing around: http://www.techempower.com/benchmarks/) but they take massive amounts of effort versus some of the newer languages.
PHP took off because of shared hosting, wordpress and pragmatism. People who were inexperienced could (1) get access to it, (2) deploy it and (3) get things done.
ASP.net survives (most would argue it didn't really take off) because if you live in the MS toolchain, it is a very nice experience.