If you don't want to pay, and you could care less about playing titled players, then don't go to tournaments :)
Apparently it does matter enough to some people
Also venues aren't free. I don't know how SCA is set up, are there random fields you use or something? I can't imagine it being free either though. I'm guessing there are ticket sales or something.
It's marketing and costs.
Prizes can draw in the higher rated players. The possibility of higher rated players will draw in other high rated players and others who want to play them.
When I first joined Chess a few years back, I asked why tourney fees were so high. He explained that high rated players will only come to earn prizes, and low rated players come so they can play higher rated players.
I understand it, in the sense of being able to explain it, but I can't relate to it at all. So, there's a guy who is really good at Chess, and he is willing to play me, but only if I pay him? And I would do that....because?
On some level, it may just be culture shock. I got involved in Chess at age 45, after spending my entire adult life in the Society for Creative Anachronism. We're the medieval folks you might see wearing armor and swinging rattan weapons. In the SCA, there is never, ever, a cash prize. There's no rule against it, but it just never happens. Probably, it's because in our sport, it's too easy to cheat, and we know that a cash prize would be too tempting for people to pass up when they could get it by cheating. We just view it as something that would degrade the sport.
Meanwhile, there's a certain code of honor among those who have been recognized as a great fighter. You are obligated to teach the young, the inexperienced, and the just plain not so good. We have specific events that are just for teaching. The titled fighters drive from long distances, with no compensation or reward, just to attend these events. In Chess, there's more of an attitude that once you have attained elite status, you can stay above the masses, and sell your services.
There's good and bad about each way of doing things, but I must confess that the other style sits better with me.