Almost all Congressional hearings are scripted, with questions and answers agreed upon ahead of the tv show. The best a Congressman can usually do is ask questions in a way that make clear to the audience that the witness won’t answer straightforwardly.
Hearing aren’t prosecutions. They are intended as information for Congress to determine budgets and rules. Since Congress no longer does those things beyond pork-barrel projects, hearings are a waste of time.
One prominent Dem said that there had never been so many people pleading the fifth or fleeing the country as during the Clinton administration. It was so frustrating, especially when the Republicans did not even make Fifth Amendment pleaders come in and publicly take the oath, listen to a question and then plead. Just imagine the historical video that could have be made out of that. Instead the Republicans just let the people's lawyers send a lettter.