I will tell you my reasoning.
I was early in crypto (went full-time 2012), so the mentality needed to do that at the time meant you had to go against what the market was saying was rational. There was a rebellious side to it as well. Many people I respected (in finance, friends, family) regularly ridiculed me, and others getting involved and doing the same worldwide. So there was an entrenched mindset of fighting established systems and expectations.
When founders (like me) were looking for good domains to build startups on, all the great .coms were taken, and were out of the price range of entrepreneurs with budgets (no VC funding available at the time). With the new gTLD program, more possibilities for digital real estate for our projects became available (coinciding with a huge increase in companies in the crypto space). Unfortunately most of those extensions were targeted to categories or specific uses (.accountant, .tools, .cooking type TLDs), and only one stood as usable for ANY use case --> .xyz.
It was the first truly open extension that really had no category/type tied to it (for usability). With xyz meaning "anything", I saw that it had a ton of potential and others did too. Combine that with the very low registration fee at the time ($2?), it was a no brainer for me to grab a few (just in case), kind of like how we bought bitcoin early, and start building on them. It was also a way to give an equivocal "F U" to the .com owners who were trying to charge us (in our view) an arm and a leg for things they were just sitting on (rent seekers/middlemen).
So .xyz kind of started as a rebellion in my mind, and then (just like crypto), went from being niche, to being important in the space. .xyz also looked/felt cool and techy, so the extension was quickly accepted and the aftermarket values started to reflect that.
.com was initially meant for commercial businesses (but became general use after), .net was for network/tech companies, .org was targeted initially to public/private orgs, etc.. In my mind .xyz was the first truly "anything goes" sort of TLD, and I wasn't the only one.
So my conclusion is that it's valuable BECAUSE of it's general use case function, not the other way around.