I do not own much. Why would I need umbrella cover?
Because a judgment can be enforced against future earnings, not only current assets. A serious at-fault claim in your thirties can follow you through your highest earning years. Having little now is a reason the cover is cheap, not a reason it is unnecessary.
Can my wages really be taken?
A portion of them, yes, under Arizona garnishment rules, until a judgment is satisfied. The limits on how much are real but the duration is long. It is one of the least understood consequences of being underinsured for liability.
Does an umbrella pay my legal costs?
Generally yes, and often in addition to the limit rather than inside it. Defending a serious claim is expensive even when you win, and for most households that defense benefit alone justifies the premium.