Your profile score does change for a reason, however HP does not reveal those exact reasons for the purpose of keeping people from manipulating the system and from people from stealing their formula. Suffice it to say, they have explained that the increase or decrease has to do with several factors such as:
(1) your activity; be it too much or too little
(2) traffic to your hubs
(3) the inter-relation to your hubscores
(4) feedback to your hubs whether it's via comments, votes or interesting, awesome etc.
(5) whether or not you have any violations
(6) publishing of hubs; you will notice that 24 hours after publishing a hub your score may increase a point or two.
and stuff like that.
What I have been told many times is that I need to moderate my activity level and don't watch the score too much so long as it's over 75. Personally I think anywhere over 85 is acceptable.