Why are companies so anal about SaaS experience? (J2 search)

I cannot quantify how many jobs I come across that are perfectly aligned with background and skill set, only to read that they require SaaS experience. It is pain in my assholes (Borat voice).

What’s so fucking special about SaaS. I don’t get the obsession. I work in marketing and I cover extremely complex and technical scientific instrumentation. I can market software. Please shut up and take my application.