I think the average age of the membership of many clubs is off putting to younger runners in their 20's & 30's who are possibly looking for a social life as well as people to run with.
Clubs can be cliquee.
Training isn't always structured to any particular goal and can't be because of the wide number of goals people have.
Clubs don't always have starter groups.
When I joined a club affiliation was cited as one of the benefits of club membership given the saving on race entry, however with membership at £25 the stipulation that a club vest should be worn £15 and now an affiliation fee of £5 (that was the point of joining a club) I would have to race 23 times per year in order to save.........£1.
One of the reasons I joined a club was to lend a hand with races, as I had benefitted from clubs marshalling races I had run, however with the suggestion that UKA are going to allow clubs to keep the unattached fee and instead charge clubs £200 or so for race permits, I can see why in the future people like myself would feel less of a need to join clubs if they were being directly charged in this way for not being a club member.
There are some very good clubs around but given that a lot are small and therefore the pool of organisers limited, I would guess that many clubs just don't have much to offer.
Forums such as this probably offer better advice and support than some clubs, not all of which have coaches.
My subscription is due soon and I'm wondering why I need to belong to a club at all.