Trump was consider a bunch of pardons for Jan6th and also for his Cabinet and those like Giuliani who worked on the election subversion and ruined their lives for him.
But trump was apparently advised by his lawyer that if they were pardoned, then they could not resist testifying against Trump. One by one they would all face jail time if they lied about what they did, for Trump.
Sure some could play the 'I cannot remember' game', but that is dangerous when you have so many others pardoned who might say you were in a key meeting, or part of a key discussion, etc. There is far more risk you will be charged with that lie when it involves so many people.
And few people, even Trump diehards, who saw how Jan6th went down, and are sitting at home fearing they might be indicted after, who suddenly get a pardon, and are free of legal risk, are going to put themselves willing back in legal risk by lying. Most will grab the lifeline and just tell the truth and move on with their lives. Especially since it looked like Trump might go down Jan6th immediate after, as McCarthy and McConnell both were condemning and blaming him.
So Trump screwed them all deliberately. He knew the best chance he had for them to not point the finger at him, was if they were at similar risk, forcing them to take the 5th instead.