As I understand it, they are not issuing subpoenas because that will throw it to the courts. That would delay the proceedings. It can be looked at either way by Bolton. On one hand he may want to testify, on the other he may just want the delay.
They are waiting on court decision which is now at DC Apeals level. If anyone thinks DC court is going to rule in FAVOR of DOJ vs HJC over getting grand jury documents and forcing WH officials to testify (judicial order) it’s a very slim chance.