Why? For PHP I sign up for one of the million LAMP ISPs, I upload a .php file with .php embedded in HTML and I'm done.
Where's the Ruby version of this? The Python version? The JavaScript version? The Perl version? THEY DON'T EXIST. You wanna use Perl or Python. You either have to use slow slow cgi or you have to RUN YOUR OWN SERVER. (virtually or otherwise)
PHP sucks, I hate it. I don't code in it unless I absolutely have to. But it's not the language that makes it popular. It's the combination of pre-installed + no setup + plus faster than cgi + works on a shared host + inline templating that's made it popular.
mod_perl? mod_python? As far as I understand them they're not useful on shared web servers so they don't fit the niche PHP is filling. Node? Ruby? They are the server rather than a plugin for apache. Again, not filling the same niche.
Someone with some chutzpah needs to step up and bring the EXACT SAME COMBINATION OF FEATURES except with a different language to the Web. They can be rich writing books and running conferences.
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Ok, now, I suspect most would want this to be in Python or Ruby but I'd argue if you really want it to succeed make it JavaScript. Because most PHP programmers have to learn JavaScript as well for their webpages. Less to learn = more likely to succeed.
But honestly, if anyone could get any of those languages to fill the niche PHP is providing it would be a huge boon over today.