IMO, they didn't want to. It was so much safer to just flap their lips than to actually do anything.
Remember - before all else - they are POLITICIANS!
Actually Glenn Simpson was called to testify and did...
https://www.scribd.com/document/368772718/Glenn-Simpson-Testimony
Actually Glenn Simpson was called to testify and did...
https://www.scribd.com/document/368772718/Glenn-Simpson-Testimony
More than once... in Jn 8 or 9 2018 and in August 2017: