I don't think anyone is talking about paying their buddies. AL is not a game with your friends though. It's a bunch of unrelated people who show up to an event, and there are just fewer people interested in being the DM than being a player. DM'ing for randos sounds like more work than fun, so no wonder they need to offer incentives to keep organized play running. An open game that the store organizes and runs would be a similar situation.
I disagree, many of the “DM should be paid” posts in this thread go beyond the limited case of AL in a store.
First, even in a store, a DM gets DM awards and experience points for DMing. Within the AL structure, they are being compensated. Plus, they get to play D&D and meet new players and get a chance to teach it to newer players. So, in the context of AL and normal D&D, they are getting paid.
Second, the game has been “monetized” from day 1. The rule books were made to be sold and it spread via the convention circuit and you needed to pay to play in a convention/tournament.
However, as I mentioned before, it is a game. Like almost all games, it is mainly played at home or in schools. Groups often form via clubs in HS and college. There is zero expectation to pay a DM in such games. Since the DM fronts the costs of most of the books and the adventures, players, as friends, often gift them the latest book or adventure, but no one pays a salary for it.
For people that cannot find a DM, and there’s is always a shortage, paying one to play has some attraction. For space in a store or a library or a game cafe or similar, a fee might be collected. In places in Asia where personal living quarters are cramped (I have lived in Singapore and Shanghai), public gaming spaces are even more important, especially after you graduate.
So I am not opposed to there being some cost to play and I am not opposed to a DM being paid, especially by a store to keep games happening on a regular basis. However, the strange fascination that some people have with somehow being a paid DM as a job path and that somehow this is normal and the supply of free DMs should be ignored is something I will never understand.