Could be many reasons right now. Perhaps the staff, knowing he is so high on the Irish, is waiting later than usual because they know his affinity for them, and would rather he assess all of his options from the major programs now rather than if and when major offers come in at points in the future. I'd rather have him check out all the major programs after him now and then commit rather than an early commit intrigued by big offers later, which happens all the time.
Perhaps the staff is waiting to see him again in person? It is still extremely early. If Junior Day comes and goes without an offer (assuming he is there), then I will question it more. But to me this is very different than a Bolden or Dorian Johnson situation. The staff has been in contact with Gibbons without, and told him that they like him and to be patient. With the others, it got to a point relatively early where they flat out said they were not going to be chasing them. I don't think that will happen with Reilly.
Just my opinion, but I think the staff is utilizing the extra time they have because of the unique circumstances to perform their due diligence on all of the OL options, and will act accordingly moving forward. If I had vbucks, I would bet he receives the ND offer by or on Junior Day. He has obviously put in the work, and deserves it. I'll take a great kid who really wants to be here, works extremely hard and is willing to do whatever the staff asks/needs any day of the week.