I've got 10 or 12 friends in USA and Canada and I've just realised they never, never comment on or "like" a pic in the albums that I put up - and I have just put up one with really nice pics in it EEISSM! 
However, if I stick a single wall photo up/upload an Instagram from my phone, and I get plenty of likes from them almost straight away ... 
I can't be so egotistical as to ask any of them "Did you see my album? Did you, did you?!" - but do any of you know if this is a known "thing"/bug/issue/whatever?