Because there are 7 Democrats on the Senate Intelligence committee, including at least 2 former prosecutors. They all get their time.
Also, the chair, Richard Burr, is retiring after this term. That makes him a little more independent than other Republicans. He was also caught by the Special Counsel’s investigation to have illegally and secretly reported to the White House the confidential list of investigatory targets of the initial Russia investigation. That could go either way: he may be strongly anti-Mueller as a result, or he might be looking to distance himself from any legal ramifications of his previous misconduct by playing this one straight.
