I started running public D&D Organised play events regularly in 2010 at my FLGS, when the D&D Encounters program started.
In those days, it was tough going. We'd sometimes have enough players to run a table, and sometimes we'd not. During the third season (Keep on the Borderlands), about Christmas 2010, the numbers dropped enough that I gave up on the program - at least in Ballarat. We weren't going to get the players.
However, despite my stepping out, others stepped in to DM and somehow it managed to get going again in the new year. It took time, but eventually we had a regular table of players again. Unfortunately, what the table didn't have was a regular DM. There are worse things than turning up to a D&D session and finding the DM has had to cancel (again) due to health issues, but it's not something I enjoyed seeing. I stepped back into the DM's chair for Season 6: Lost Heir of Neverwinter (August 2011). And I ran every season from then on. We never had the experience of having to cancel a session again due to lack of players, and slowly - ever so slowly - we began to build the player base.
This really became apparent when the playtest started. The numbers began to build. For the Vault of the Dracolich Game Day event, we had three tables. The following season had two tables on a regular basis. By the time we reached Scourge of the Sword Coast, we had 3 tables. Dead in Thay? The last session had 4 tables, and when Hoard of the Dragon Queen started, we had five tables on a regular basis. That's continued since then, although numbers have dropped back from their high watermark of 42 (second session of Hoard). These days, 30-35 is regularly achieved - although it can take a sharp drop when public holidays mean people are spending time with their families.
I know for a fact that many of the people who play in these events have made friends with other players and have started up home games with them. Some of the players who have dropped out have continued playing the game - in those groups. This is the great strength of having organised play in-store: it allows friendships and groups to form, in the same way that groups often form at universities.
I also know there are a lot of players in Ballarat who don't partipate in OP, but still play the game. How many? No idea.
Part of the point of this is that I've had some of the players participating in this OP group for several years - four or five years in some cases. I'm extremely supportive of how the AL now allows several modes of play: you can play in the long campaigns (Princes, Tyranny), or in the short adventures (Expeditions), or in the small beginning-level games (Encounters). That we can now run extended games is a huge bonus; many of the long-time players were very sick of having every Encounters season being levels 1-3.
AL isn't for everyone, but there's a joy in playing with a wide range of players that you won't get if you're only ever in one small game group. D&D allows a wide range of play-styles; AL is one of those styles, with different strengths and weaknesses from the others.
Cheers!