REI can be competitive on their core products which they know they can sell a lot. On the other hand, the Mr. Heater is not something they sell a lot of, thus they don't bother making it competitive. Stores don't even have it in stock, it has to get shipped to the store... I'd guess they don't actually have any and orders get drop shipped directly from the manufacturer. That increases the cost for REI, compared to Amazon that can afford to stock them since they know customers actually go to Amazon to buy them. So there are plenty of items listed on REI's website, as well as most other gear sites, that they never carry in store but are happy to sell you online if you really want to pay full retail price.

And the Coleman dual fuel price is nearly the same as REI.

https://www.amazon.com/Guide-Series-Dual-Fuel-Camping-Stove/dp/B00QMW5H76

Note that the normal price is $130. Yes, it's on sale for $67... that's the power Amazon wields, the ability to lower the price to beat all competitors. And REI is not a competitor here, Walmart is.

REI can't compete with Amazon on many products, but again, there are plenty of products that people go to REI to purchase. Patagonia and Birkenstock are two that can't legitimately be purchased on Amazon (or Walmart for that matter). Since there are products Walmart can't sell, they actually purchased Moosejaw to get a foothold into the higher end outdoor gear market. So if someone looks for Patagonia at Walmart, they can be redirected to their Moosejaw subsidiary.

Anyway, you haven't uncovered a great conspiracy, it's pretty well known. It's also well known that REI is expensive so many people wait until one of the coupons comes out. With the 10% dividend, and 5% for using their credit card, there's a lot of incentive to buy at REI, especially for stuff you can't actually get from Amazon or Walmart.