Please don't mistake me: PHP-the-language is not well-designed. And we absolutely would never have gone down this road if we didn't have a metric ton of PHP to run and continue developing.
There are a few things PHP gets accidentally right, though, and one of them is the execution model. Each request starts with a brand new empty PHP environment; runs in a single thread to completion; and must keep persistent state off to the side in a database or memcache or what have you rather than in language-level objects. This turns out to have been a really good set of decisions. It lends itself to a nice tight development loop: instead of save/recompile/restart the server/test, you basically save/load the page. It's easier to remember what the heck you were doing when you get feedback on the code you wrote in 500 milliseconds.
There are a few things PHP gets accidentally right, though, and one of them is the execution model. Each request starts with a brand new empty PHP environment; runs in a single thread to completion; and must keep persistent state off to the side in a database or memcache or what have you rather than in language-level objects. This turns out to have been a really good set of decisions. It lends itself to a nice tight development loop: instead of save/recompile/restart the server/test, you basically save/load the page. It's easier to remember what the heck you were doing when you get feedback on the code you wrote in 500 milliseconds.