It's not unusual [1] for a provider of services to be paid later - if you happen to be in a job you've probably encountered the concept as companies tend not to pay employees daily in cash. If the money's coming from the brewery, the landlord is probably going to prefer to have them deal with you. I have had a split payment on one occasion, 50% or so in advance and the rest a week or two after the gig. With agencies, they're not likely to want to pay you before they've got the money, which doesn't seem unreasonable.
[1] A brief attack of Tom Jones there