I work in the wedding industry. The big limiting factor for wedding rentals is that most people want to have a wedding on a Saturday night, and there are only 52 of those in a year. Most weddings are concentrated in the spring/summer, so you end up with a much smaller number of dates to actually work with. For a higher end venue (the stuff in the $5000+ range) in my market the rental fee will also include cleaning, day-of planning/setup, and valet parking.
Sunday brunch weddings are starting to become increasingly popular for this exact reason. Everyone wants a pinterest-perfect wedding, but not everyone wants to shell out $4k just for the space.
The last puzzle piece to the price is that wedding parties can be some of the neediest customers to work with, and it's not like you're going to get a lot of repeat business. In fact, friends of the bridal party often won't want to rent your space specifically because they've already been there for a wedding.
It's still a viable market I think, but you have to realize you're not going to get that $5000 price tag 365 nights a year, or even 52.