Just like any service, Facebook has a certain amount inactive accounts. It can be that the owner has died, lost interest or it's a spam account that's no longer used. Facebook is now having a spring clean where they will be removing inactive users from Pages' like count.
At the moment accounts that are on purpose deactivated or memorialized after death are currently still factored into the "like" count for a page. This is set to change in the next coming weeks and Page admins should expect to see a small dip in their number of Page likes.
Facebook says it's important to remember that removed likes represent people that were not active anymore on Facebook and the Page stats are becoming more meaningfull now. The Facebook like count will be giving a better reflection of the number of Facebook users who are actually interested in the service, product or person associated with the particular page.
The benefits according to Facebook:
There are two primary benefits to removing voluntarily deactivated and memorialized Facebook accounts from Pages’ like counts:
Business results: Removing inactive Facebook accounts from Page audience data gives businesses up-to-date insights on the people who actively follow their Page and makes it easier for businesses to find people like their followers through tools like lookalike audiences.
Consistency: We already filter out likes and comments generated by deactivated or memorialized accounts from individual Page posts, so this update keeps data consistent.
Important note though: when a deactivated Facebook account would be reactivated in the future, the like count will come back.