I never had to pay state taxes in California due to my income being below poverty. Why do I have to pay taxes in Oregon?

Oregon has different rules and different exemptions, tax credits, and deductions.   Each state is different.   In terms of taxes, Oregon levies lower income tax rates, making it more favorable for individuals with higher incomes.   

For Oregon residents, your income tax is based on your taxable income from all sources. The income tax for nonresidents is based on taxable income from Oregon sources. If you're a part-year resident, your income tax is based on taxable income from Oregon sources while you’re a nonresident plus your taxable income from all sources while you’re a resident.  2023 charts