This looks a likely a big part of it, and then we also have reports from MSNBC that at least some of the evidence being presented against him came from one of his lawyers. It could have been a former lawyer and not one of the two that recently resigned, but if it was one of these two they would have to resign or risk personal legal consequences.

Trump seems to have taken the view that plotting illegal things with his lawyer is smart due to attorney client confidentiality (see Cohen), not understanding that confidentiality specifically does not protect discussions related to new crimes. No one can force your attorney to disclose that you told him you were guilty, but if you ask them to help you suppress evidence or intimidate a witness, nothing stops the attorney from turning you in, and they have reasons to do just that as you’ve just made them complicit in your new crime and that is not protected by privilege.