Why do most people seem to have a negative opinion of Macanudos?

I agree with all of the above. He likes Macanudos, great! However, it'd be cool if you could broaden his horizons with a stick or two. CI regularly has deals where they throw in a 20 count humidor, why not get something like that for him so that he has a new humidor? You could even fill it with some of your favorite smokes.

[captain53]

Nothing at all wrong with Macanudos, they are a quality cigar. Just for some reason BOTL's seem to declare war on certain cigars because many for whatever reason don't prefer them other examples would be Ghurka and Graycliff. Nothing wrong with any of them and they sell in huge quantities worldwide. Macanudos tend to trend on the very mild side so a lot of long time smokers don't much care for them.

All you need to know about cigars is what kind tastes good to you.

If it is what the man enjoys then get him some more of them and since he is your Uncle and there will come a day that you would give anything to sit down and enjoy a cigar with him then accept his Macanudos when you are with him and appreciate the time spent. I say this from experience.