Probably PHP is still not the language of test engineers. Users are more often to choose Cucumber + Capybara (in Ruby), JBehave, and others. Ruby and Java have official Selenium bindings, thus many enterprise customers choose them for testing.
Personally I didn't use Cucumber, but used RSpec + Capybara, when I was working with Rails 3.x Now I switched to Minitest. For frontend development I was using Jasmine and QUnit.