When shared hosting was the norm. mod_php was much faster than CGI and a lot safer to use because usually processes in one virtual host did not affect processes in another unlike with mod_perl and the like.
The strong selling point of PHP for a long time was cheap hosting. Combine that with a fast learning curve and you're set.
Nowadays, it's not so clear cut price wise, but PHP took a strong advance in term of user base - look at the number of libraries, projects, and jobs (!) available in PHP, vs python or ruby.
PHP followed a very uncommon path. Features were added as needed, in an incremental fashion. Nice syntax is never a huge problem, though that's probably most people complaint. That said, it isn't worse than its "contenders" in terms of feature set. You get a decent object system, lambdas (note that they'd been there for a long time, but it's more convenient now), a wide range of bindings.
It's not pretty, but it does the job in many cases.
But, anyway, if you're really looking for a good language (something efficient, where you don't have to spend hours to spot a stupid bug), skip the dynamic ones altogether, and go for as much static analysis you can get.