It boils down to design, materials/construction, durability, and support. Making a great product takes design teams and engineering teams years to optimise. You're not buying the price of materials and construction. You're buying all the overhead it took to get to the final product.
The two leaders I regularly see visiting various offices are Herman Miller and HumanScale. Worth it if you have the wonga. Virtually every chair they make is ripped off and sold for less by others. (Design patents are virtually unenforceable.) You're likely getting only 0.5 of the 4 listing above if you purchase one of them. They probably won't be as comfortable, too as both companies really sweat the details. 2 mm here and there make all the difference in the world.
There are inexpensive alternatives that may be as good to you. I don't want to imply leaving the top tier means everything else is rubbish. It's an odds thing. You're more likely to be happy after 10 years sticking with the top tier. Some may make the case going through 2 chairs in that time frame is a better thing. it's what you like and want to spend.
I recently was pricing an Arne Jacobsen "egg chair". Herman Miller (in leather) approached about 15 times the cost of an Amazon sold knock-off. Love the look, but it's placed on my "after winning lotto" list.