While diversity in the arcade would be nice...you have to remember a couple of things:
(1) A lot of the Japanese cabs are privately owned and rented by OCE. This also ties to the next point that: while new games come out, what makes you think it would be worth it for an owner or company not to have it in a Round One or D&B instead of FanimeCon?
(2) As a union venue and one that charges for everyhting, the cost of power must be incredible and while people talk about profit (which maybe OCE does), it's hard to think that FanimeCon makes enough to pay for power, OCE Services, etc. and turn a significant profit.
(3) If it was my cab, I wouldn't want any food or drinks near it. The late night crowd also has individuals that are intoxicated and more likely to abuse the machines (that's a lot of risk and loss to consider). I remember seeing a post that must've been deleted about the con and it's vendor, but one thing is for certain, if AX doesn't do a freeplay arcade either, there must be a reason it doesn't work for animecons. not to be a troll, but "FanimeCon and AnimeExpo are not mainstream"? ...really?
Just to chime in and as a aspiring event planner...What might work for one event might not work for another:
1) It'll be up to the company or private collectors to pick up new games if they think their clients/attendees will enjoy it and/or there's ROI on it. Not just for arcade cabinet providers, but also video game equipment providers/event support operators.
For Round One, I heard they work directly with the game companies involved due to licensing (and Round One is from Japan after all so I imagine 1:1 on policies).
2) We worked with OCE (and any company really) in understanding power requirements for equipment on-site. For Gaming Hall, we want to be 110% sure there is enough + a safe buffer to avoid issues during 'Con.
3) As the Gaming Hall is a 24hr operation, it comes with operational challenges and the late night crowd issues are ones we are 100% aware of. We do take active measures in making sure our attendees/staff/equipment/venue items are safe during the late hours. We train our staff to call in help the moment we see an intoxicated person(s) causing trouble. As gamers too...well, the feeling is mutual.
Food and beverage around arcade (and eGaming) stations is already prohibited as per our area rules (sealed containers are allowed).
There are other anime conventions outside California that have their arcade on freeplay. Most notably as the OP said, MomoCon, MagFest, ColossalCon, but also Anime Boston / Anime Central / SakuraCon + various others. The spirit of this post is asking why we have not done so, and this is one that requires careful review and consideration internally.