Re: This needs to stop
I must admit that my first thought was to wonder why anyone would voluntarily attend a PHP conference and if perhaps masochism is a more masculine trait.
However, "(group X) didn't apply so it's unsurprising they're unrepresented" is not "common sense". It used to be said a lot about the (lack of) ethnic diversity in pubic services: turns out if you place your job advertisements in places where they'll actually be seen by people from ethnic minorities then they do actually apply. If you fail to understand the limited reach of your communication network, you're not going to make any effort to make contact beyond it.
I have no idea how the call for papers was circulated, but if you want a representative response, you have to put some effort into approaching a representative sample.