Because...
1) PHP doesn't have a mareketing budget like Microsoft.
2) PHP is a relative newcomer when you compare it to languages like Perl and Python.
3) Microsoft hasn't mentioned PHP (its mentioned Apache, Perl, and Python, but for some reason, they haven't yet compared their ASP to PHP, probably because they no better) and therefore, the press haven't jumped on it.
4) It is slowly gaing populariy, do a search on dice.com for jobs with PHP in them..and you will see its growing.
5) PHP3 was more a play language, and it hasn't been until PHP 4 that we can really start taking it seriously.
6) Windows support is still inadequate. Whine all you want that Windoze sucks this and Business that use it are st00pid, BUT!, remember, its these same businesses that use Windows that DON'T care about supporting any Movement like the Open Source movement as much as they care about supporting their own business that are making the decisions. And if their office is running on Windows, well, guess what. And until Linux gets a decent desktop version out that is as easy to learn AND use as Windows (average users don't care what a kernel is, don't care for command line, and like GUI's, which are the reason computers are so popular...), Microsoft will continue to dominate the business Desktop and Home user dept. And that means Businesses will continue to use MS Office, and its a lot easier to install a Win2k server (which is actually a good OS), cheaper to maintain it (MS people generally get paid less than their OS counterparts, yeah, it may be different where you live, I take this from my personal exp and from what I have heard a lot of other poeple, including staffing agencies, say), much easier to find people to maintain it, and is usually much more compatible with the Win machines in the office. ASP then becomes a natural move.
7) More people know PHP than ASP. So, if a PHP developer leaves a company, than are left hardup for a new developer, unlike ASP.
These are just some reasons. Take it as you will..
Jason
www.newbienetwork.net