I am going to try to answer your question with a completely different answer than every other one I have seen. You asked WHY. Not what makes the most sense, but WHY. Why do some people have far more money in electronics than speakers.
I think for the almost all audiophiles, whether they admit it or not, it is a matter of logistics and retail therapy. Audiophiles buy equipment because they like to buy equipment. It’s retail therapy for them. Just the simple act of something new is a psychological reward. Come on, admit it, you all know this is true.
That brings us to logistics. Most amplifiers, and almost any other product are easy to buy, pack, and ship. There are 300lb amplifiers but they are the exception. Even a 75lb amplifier is fairly easy to pack and ship. Speakers are a pain. They are heavy, they are awkward, they are difficult to ship, if buying used, shipping can be a substantial part of the price. But the audiophile needs his retail therapy fix. The best choice would be to upgrade the speakers, but that take a lot of effort. Even selling a used pair is a lot of work. So, instead, the audiophile upgrades their DAC, their pre, adds some high end cables, and before you know it, those $5K speakers which represented a large portion of their system, are now $5K speakers in a $30K system.