I never quite understood how the traditional airline business got themselves into all this hoopla. You certainly won't find any of these options on Easyjet etc, where it's pick from their standard basic offerings, or go without.
It's called providing a service, especially on long haul routes. Special diets have always been a part of legacy carriers especially when it comes to vegetarian options.
If you really do need a "Halal salt-free low-fat", or whatever, buy your own in the terminal at departure.
You would never get it through security.