There are pretty significant difference between ruffle con and the UK events. First of all, uk and us is pretty different in terms of the service industry and event venues.
You aren't going to find decently classy places to have an event in the us without shelling out a ton of cash - event spaces are newer and geared towards either corporate events or weddings, which means either bland and bare minimum or way overpiced because the wedding industry is insane. Wanting to have the hotel attached to the convention space is even more difficult to find, and from what I've heard rc doesn't want to move to a space where the hotel and event location are not attached.
In the uk it seems like not many of the event spaces have a hotel attached, but the uk is much more pedestrian friendly and generally safer for Lolitas/alt fashion people to be walking to and fro.
I don't have numbers on how many tickets/people went to Omnia Vanitas - their Facebook page says just north of 300 people but I hadn't found a way to verify that (I wasn't there so I can't say if that's accurate or not, maybe someone else can chime in here). According to ruffle cons site they had 480 attendees this year, over 50% more than what I've found for Omnia Vanitas.
If the goal is for rc to emulate street fashion europe's events then maybe they would have to limit the number of tickets sold.
If they had 508 attendees last year (found this info on their about page) and it sounds like last year was Abit better provisioned, is possible they were in the red last year if they spent too much on gift bags or whatever swag, and they tried to cut it down this year to make it up, but possibly they cut the budget down too hard. It's hard to make a guess what happened, it seem like the people who run it don't put much info out on how they mke decisions