How do you know that they weren't too busy? Shopping isn't always a big lark, or maybe they were shopping *with* someone- a friend they wanted to catch up with for eg. I wouldn't automatically think it odd or get upset. Will you see them at Xmas? If I was interstate for a wedding for only one weekend and was going to be back for a quick Xmas visit in a couple of months I might prioritize friends I won't see at Christmas over family.
I've gone longer than 10 months seeing one of my brothers and we live a few suburbs apart! We are close, just both busy I guess.