The resorts I go to don't build their own jibs, in fact I don't think i've ever been to a resort that build their own, and i've been to quite a few. You talk as if building your own rails for a resort is free. It's not, materials for it isn't cheap, and on top of that you can add the hours it actually takes to build it. Buying them ready made is a good, durable and cheap alternative. Not every park manager is a welder and carpenter.