At least with Linux I don't have to wait 6 hours for all my software to finish compiling. Think about all the trees that are unnecessarily cut down because of all that compiling. And support for Linux is much easier to get than support for OpenBSD.
TLDR: Passenger takes a more holistic and integrated approach and is a lot easier to use. It has superior management and administration tools, superior robustness features, superior security features (e.g. sandboxing through user switching), better documentation, uses less memory, etc.
Also, this is why anybody would want to use Passenger over Puma: https://github.com/phusion/passenger/wiki/Puma-vs-Phusion-Pa... (or vice versa, for that matter)
TLDR: Passenger takes a more holistic and integrated approach and is a lot easier to use. It has superior management and administration tools, superior robustness features, superior security features (e.g. sandboxing through user switching), better documentation, uses less memory, etc.