Why mod_python is oop but mod_php is not ?
Example :We go to www.example.com/dir1/dir2
if you use mod_python apache opens www/dir1.py and calls dir2 method
but if you use php module apache opens www/dir1/dir2/index.php
Because mod_python is abstracting the URL into a "RPC-like" mechanism. You can achieve the same in PHP. I always did it by hand, but I am pretty sure there are prepackaged pear modules for this.
Note the mod_python behavior is not forcibly "the best". It all amounts to the type of design you want to give to your application, and how it behaves to the clients. As far as I see, the mod_python approach assumes that for every URL you have a function, like mapping the module structure into a URL tree. This is technically not a particularly nice approach, because there's a tight correlation between the technology you are using (mod_python) and the URL layout of your application.
On the reason why, theres' no reason. Some people like one food, and some other like another. Design is, in some cases, a matter of taste and artistic choices, not only technical restrains.
mod_php vs mod_python