Some broad answers:

1. Fee is higher than people are willing to pay
2. People don't trust the experts
3. The experts don't exist yet
4. People have no idea how to find the experts

What "people", what "experts" and in what field? What industry? Can you provide any additional context for the question?

Is the premise that "people" never hire "experts" or are you wondering about those cases where they don't? I find it hard to believe this former is universally true.

Experts are expensive.

I'll speak from my experience in engineering.

It is extremely difficult to find experts. There are just not that many people around who are both smart and knowledgeable enough to solve high end engineering problems. This is why the vast majority of complex problems are solved by very few people, with the rest existing to support them.

10x'ers are real. Except it's worse than that. The tip top can solve problems the median person will never be able to.

Second, like everything, expertise exists on a continuum. Since the best of the best are radically more talented than the median (who you could still even call experts) or even the 90th percentile, you want the top ones.

It's just very hard to tell them apart in an interview. You can try the standard interview questions, but that's not very discriminatory.

I am an "expert" in my field. But it's not because I'm the best in the world at networking and servers. It's because I am one of the few in the world who knows this highly specialized system setwork, how it integrates across VPN, and a bunch of other niche stuff. Sure, any donky with basic linux and TCP/IP skills could do my job, but it'd take years to train them on this particular setup. And that's because experts are mostly this: highly specialized in what they do well.

We have multiple experts at my job, and we frequently have to call each other due to ineptitude in what is outside of what we normally do. Ask me how to right click on a mac and I'll come up short. Ask me how to fix some broken O365 setup and I'll have to guess based on 20 years outdated IMAP setups that I haven't touched in one and a half decade.

It's easy to find experts. But experts in the exact thing you need are rare.

Because experts usually know their worth and charge accordingly.

Thats a heckuva false premise

I'm an expert at fucking my life up. I have no idea why anyone won't hire me.

We’re pretty expensive. Honestly you have to be good at something to understand the real value an expert can bring.

Money probably even if it means a lack of quality and/or done wrong. Might be more expensive in the long run so its kinda ironic

What makes you think they don't???

I often don't hire an expert to do certain tasks. Here are three common reasons:

• I don't trust any expert that I can hire
• I can do the job adequately and I consider the expert too expensive relative to the value of having the job done very well
• I want to learn how to do it and so I want to practise

Sort of broad, but you'll find more experts working for Governments than at corporations. Corporations can't or won't pay top dollar to put experts on the payroll. They might hire one as a consultant if the price is right.

Most experts not involved in Government are self employed or do contract work.

I can figure it out.

Because they're worried the experts might discover that they've been "winging it" all along!

• Sometimes "experts" suck. I've had 2 projects done to my house that need to be re-done, they were so bad. I would have been better off investing some time into learning to do it myself, which I now have to do anyway.
• Having experts do my camper van conversion would be ridiculously expensive. Same for buying pre-made things. There is a lot to learn about floor, insulation, wiring, charging, cabinetry, water, storage, etc. But learning that is one reason I'm doing it myself. Mistakes still don't add up to even one piece that pre-fab or shop expert would charge. For example, a galley is about $1200 (sink, fridge cabinet). I built my own for ~$200 and got most of it done in one day.
• There are some experts I will trust. I trust one bike shop to do my shock service each year because frankly it's a messy hassle for me to do it myself, and If I screw up, I buy a new $1000 fork. If they screw up, they buy it.

Because, more often than not, we have a very hard time determining whether someone is truly an expert, or just good enough to do the job.

Even if you found them, more often than not their motivations aren't to work for megacorp in a major city. They might be married, with kids, and enjoy where they're currently at. They might be happy enough building shitty web apps over working at a FAANG company. They might have tried working at the top of their career, realised it was more trouble than it was worth, and decided "nah, I'm good".

Because they don't know where to find the Experts Lounge, duh. /s

There's a strain of anti-intellectualism in America at least, and a lot of people don't "trust" experts.