Railtie initializer executed on startup, but block is never invoked

Yeah, I kinda wondered whether an official initializer via on_load would be the more kosher option, if I could get it to work. I load the railtie from this file in lib:

module BulmaForm
  require 'bulma_form_rails/railtie' if defined?(Rails)
end

I originally loaded this via an explicit require, but now that I’ve moved everything into a gem, the Gemfile takes care of that. And interestingly, the on_load syntax now works just fine.

So something is different about initializing from a gem that makes the kosher way work?