4 year old suckles blankets

A little background, Osiris is almost 4 and I've had him since he was about 3 weeks old (litter had to be supplemented and limited time with bio mom because she was not a good mom). He is constantly suckling on the soft blankets on my bed, the couch and even has his own baby blanket he's had since birth that he will do this with. Is this just a normal comfort thing? I was thinking maybe it has to do with not having a traditional puppy experience? The only other dog I had that did this was my prior Dogo Argentino who came to me via rescue at 9 days old whom I bottle fed and as taken care of by me from then on. Or maybe a combo of both self soothing and not having bio mom as long he should have? I think it's kind of cute and don't really discourage him from doing it but do try to remind him to do it with his designated blankie and not the ones we use. It's not a big deal to us but not having soaking wet blankets is nice=) Just curious if anyone else big babies do this too and why they might do it? Those are the only reasons I could think of why mine might do it. He will do it for an hour+ if I let him.