Why do ppl buy travel trailers when it's obviously not a wise purchase
Because the industry finances them over a 30 year term. That is not a misprint.
On your typical 25 foot $19,999 travel travel trailer there is 25% gross profit. Ever wonder how all those zillion RV dealers stay in business? Consequently, the monthly payment on that trailer is $133. per month for 30 years. PPL block out the "30 years" part. "This will be great for the kids" and it is, for the next 7 years, and then the kids out grow it, the thing has fallen a part, and is a worthless POS and they still owe 23 years on it. Welcome to RV land. 
Thats one math for sure. But it shows so your argument is right.
But there is also the other math, where people buy a trailer and pay for it in a year or 2, or also buy a good used one. Ill use your example above since thats the price we paid Spring 2009. Our montly payment is higher than what you mentiioned, because we want to pay it off. Since then we have also put down 2 tax refunds on it, as well as the money from selling out tent trailer. We are now down to $9000 owing, and will probably have it paid off my this time next year, give or take. By the time the kids outgrow it will be about 8 -10 years (our youngest is 8
In 8 years I really dont see it falling apart, out 10 year old tent trailer was still in great shape because we took care of it, and got a good price for it because of it. And if we decide to sell it in the futre, I really dont think it will be a worthless POS as you put it.
It would be the same that it makes no sense for people to own a boat since in Canada you can only use it in the summer months. So what, in those months you can use it for what you want to do, fish, water ski, etc, etc
