It's just capitalism dude, plain and simple. If seeing the prices honestly gets your undies in a twist, then just don't look at them. I'm not speaking specifically about you, since I don't know you, but one of the biggest problems with 21st century western societies is that people living in run down apartments look at people living in nice houses and would rather spend energy complaining about what they can't have or control, rather than focus that energy on being happy with what they do have or working to improve their own situation. That's why so many high schoolers and college kids in this country want free education, free medical care, and $15/hour to work at Burger King or bag groceries. Capitalism doesn't work that way and an economy is not sustainable that way either. The money has to come from somewhere.
As far as rational decisions go, I think you contradicted yourself in that one sentence. You can't say "Most people who would buy have already decided they're going to [...]", and then in the same breath say that those same people are "[...] waiting with baited breath to throw their money at them [Mirai] because they know they don't haven any time for rational decisions." Think about it; if someone is waiting for the Mirai sale to open with $5,000 of disposable income at the ready, then yes, they have likely already decided they're going to buy something. However, I would certainly not say they don't have time for a rational decision. They already spent time before the sale making a rational decision about whether or not they would spend that kind of money. I can't afford a $5,000 tree, but I would not buy even a $500 tree on a whim. I would think about it rationally first. Knowing that Mirai trees sell out fast, I would decide before the sale if I was OK with spending that amount of money within 5 minutes of seeing photos of a tree.
Can everyone who owns a Yeti cooler actually afford said cooler? No, but they bought it anyway. Yeti doesn't care. They just want to make money selling coolers. They don't care if you bought a $500 cooler instead of replacing that set of bald tires on your car. Likewise, Mirai doesn't care where your money comes from. They sell trees to make money.
Masters and professionals in their field often make the very difficult look very easy. It's called training, practice, and natural ability. Usain Bolt runs like he's not even trying. Guy Fieri grills up meat like he's not even trying. Michael Phelps glides through the water like he's not even trying. Ryan produces amazing looking trees like he's not even trying. See the pattern?