Instead of hundreds of poorly qualified people why canâ(TM)t we have someone who actually knows the products to smash through tickets
As someone who worked for years in support (a long time ago), it's a classic case of "intersection of sets".
On one hand, you have the set of people who actually know the products. On the other, you have the set of people willing to work in support, manning phones.
The first set is more or less inelastic. The second set can be increased somewhat by offering high salaries, but that's limited because if you increase them enough, you would reduce other sets (e.g. people who know the product but work in other areas related to the product). For example, if the helpdesk agent salary reaches or exceeds the backend support salary (that is, the engineer who is on-call), the latter would move to the former, and then you'd have a lack of engineers who know how to fix the product when it goes kaboom for some reason.
Which means it's all a complicated dance.
I worked in direct support (taking phones) back in early 2000s, and did it for a limited time, because it was an entry job and the good ones (with enough willingness and brains to move up, which wasn't a high bar) were quickly snatched to fill other positions. I remained linked to support departments, but I was no longer taking direct calls. At any rate, the struggle to hire even remotely competent agents was real. Scraping the bottom of the barrel was continuous, and the attrition was enormous, sometimes exceeding 200% per year.
There's the answer to your question.