A partial answer didn't take long: There wasn't enough subsidy to compensate for weak demand. Maybe Salem doesn't really need air service.
According to the Statesman, Seaport will stop service on July 18th.
The Oregonian adds that the end of Federal subsidies appeared to drive the decision:
[Newport] city officials offered free housing and fuel discounts, they waived tie-down and landing fees -- but in the end, it just wasn't enough. Four months after state and federal subsidies stopped, SeaPort Airlines announced it will stop flying out of Newport effective next Monday.Salem had also waived landing fees and offered several other subsidies.
So what do you say we forget chasing after air travel! Let's make Salem a world-class bicycling city!
(Lots more people bike around Salem every day than apparently fly Seaport...just sayin'. Smart Cycling Clinic by Jeff Leach)