Facebook friends are often more motivated by attention seeking, networking, and glamor or prestige by association than genuine concern for the well-being of their declared "friends".
When the pursuit of such measures of social credit in the eyes of others, or some other utility or social value is the primary motivation for the claim of "friendship", the concept is cheapened and trivialized.
Even worse, increased access to one's social world and personal disclosures is achieved under the auspices of friendship by some who would use that access to increase their effectiveness in undermining you in other venues.
Such disingenuous elements of "friendship" were once well understood and branded as "two faced". In today's world, the social acceptance of sloppiness about the claim of friendship tends to increase social tolerance for the two faced duplicity that was better recognized and condemned for what it was in times past.