Being deposed and sitting for a public hearing are two totally different things, Crepitus. At a public hearing, members of Congress have only five minutes each to try and get Hunter to explain what he did to earn all of those millions. At a deposition the questioning continues until the person being deposed either answers the questions or takes the 5th.
Watching various public hearings lately has led me to the conclusion that they are largely worthless. Witnesses like Mayorkas know that all they have to do is talk in circles for a few minutes and then the five minute time allotment is up and they still haven't answered anything. Wash and repeat. FBI Director Wray does the same thing. Claim it's an ongoing investigation and you're not free to speak about it...ramble on about that for a bit as you run out the clock. Wash and repeat.