That's my point though. It is an active investigation for obstruction of justice. Lawyers speaking directly with investigators unless requested is generally not the usual process and potentially misconduct.
The FBI has never formally announced that they are investigating the president for obstruction of justice.
We have deeply sourced articles that state that he is part of the ongoing investigation, but it is not official. Trump's lawyers cannot be committing malpractice for offering information into one investigation (the Russia thing) that may contradict another investigation (the obstruction thing) that doesn't exist.
As always with goings-on with this stuff, there are things that we "know" because they were revealed to the press, and things we
know because they were aired out publicly in a hearing or by one of the president's tweets/interviews.
Trump's lawyers are attempting to do this now for likely quite a few reasons, one being that they want Trump to appear willing/innocent, 2) the investigation is underway so Mueller likely has an incomplete timeline, 3) they want to get a potential inkling of what he knows, 4) the president gets to 'answer questions' while not under oath.
Even a PR statement like "The FBI has not confirmed that the president is under investigation, fake news" would be seen as a win for Donald.