First,
Lerner was willing to talk - without immunity, in depositions with committee. Issa didn't want that. He wanted the cameras. He wanted the show trial -- it's about the dog and pony show.
Second, your post excludes the obvious, which is included in your link.
"[A] prominent white-collar defense lawyer, Robert Luskin of Patton Boggs, said he did the same thing in the face of a highly-partisan congressional probe into the Whitewater matter during the Clinton administration.
“
Our view was that the DOJ was genuinely and sincerely interested in an honest and thorough investigation,” while a GOP-led congressional panel wasn’t, said Mr. Luskin. So his client “testified without condition to DOJ and took the Fifth with respect to the committee.”
One frequent concern for witnesses appearing before hostile congressional committees: Lawmakers can set perjury traps for them, hoping to trip them up. Mr. Taylor said that wasn’t a concern for Ms. Lerner."
Former IRS Official Lerner Gave Interview to DOJ - Washington Wire - WSJ
It doesn't take a rocket surgeon to understand kangaroo courts -- which is the way Issa is running his "investigation", that start with the premise 'we plan to hang you on high,' and dubiously release cherry picked emails and transcripts (which later turn out to refute what they purport, when seen in whole) and especially after that despicable display of Issa shutting off the mic on the ranking minority leader like that...are not about fairness, justice and truth.