Because I didn't want to. My computer is 100% post consumer recycled content, and most importantly, it's suitable for the task.
Regarding Rakellion's comment about someone who uses a $100 computer not being suitable for this site; he's probably right. Technologists and hackers have turned into consumerist n00bs. A technologist now is someone who buys the most expensive kit, and gets stuff to create envy amongst the other facebook drooling "technologists", instead of making sensible hardware do tricks, and using one's brain to make the computer better.
You seem to expect people don't have any need for systems with higher performance.
According to you, if I buy a MacBook Pro, I'm simply a noob who doesn't understand computers.
I should be able to get buy with a $500 Celeron-level laptop just fine. Of course, I don't mind waiting years to process 500MB PSD files or batch convert a selection of RAW files. The inaccurate display will surely cause no issues, and obviously I can adapt to the quirks of the keyboard and touchpad. The battery life is a non issue so long as I remember to be near power outlets.
If you only type and browse, spend what you can justify. That my $500 Acer is actually still kicking 8 years later is impressive, but the last 4 years its been rarely used, and mostly useless. Typing notes and studying and wasting time? That was all I needed at the time.
The argument that everything is Chinese and cheap really doesn't matter - to get the same chipsets and internal hardware in any laptop will basically have the same cost across the board. You might have a slight charge for premium build, but the cost of a Mac compared to a throwaway Dell is not related to build or materials, rather the increase in performance.
If you are after performance, it is really just down to Mac or Windows (and you can have both).
If someone just wants shiny, then I agree with your post. But in reality, outside of a college town, the majority of MacBook Pro owners you see at a coffee shop are likely involved in arts, design and/or publishing. And some, including MBA owners, may just want what they want.
Quite a few are just chasing pretty things, but quite a few actually need and use that performance.