Why?
Left PHP because I lost confidence in the language. I cannot write 10 lines of PHP with out feeling nervous of the edge cases I have missed.
Also, some exchanges with the 'core' developers of the language completely convinced me that the language is not going to improve. Their behavior and competence felt like they are just 15+ year old kids doing programming language work on the side. And the community! I cannot think about that without throwing up. Over engineering and bike shedding is the norm. Even the so called community leaders are UTTER MORONS. Without exception. No. I am not exaggerating [1] and that is not the only one, just the most recent. Also, please note that I am some one who started with great respect for these guys...
That is my opinion formed by closely following everything related to php, mostly from /r/php for 4 or 5 years.
Regarding MySQL, I was one bitten by MySQL when it didn't allowed me to use the same temporary table more then once in the same query. So that left me with a bad taste. And once I tried PostgreSQL, it felt quite a bit simpler and seemed to be lot more capable than MySQL.