Why is it not? It's considered a state wide income tax.
From Oregon's own Tax Professional’s Liaison Meeting in 2018 they conclude that it should be fair game for federal Sched A but not state OR-A.
https://www.oregon.gov/dor/programs/taxpro/Documents/tax-practitioner-meeting_07-18.pdf
"The statewide transit tax is an Oregon income tax and can’t be included on Schedule OR-A as state taxes paid. It can be included on the federal Schedule A." -page 6, 4th bullet
