It is super expensive to hire someone. The costs are enormous.
Let's take a hire that will make $10,000 per month, nice round number.
Someone in HR has to write the job description. This takes the HR person's time, the hiring manager, the hiring manager's boss just to get the information for a job description
Job description cost with hiring manager: $500
Job description cost with hiring manager's boss: $500
HR person's time to talk to hiring managers and to write the job description: $1000
Job board postings: $250
Headhunters if found through them: $30,000 (3 month's salary)
Corporate career page posting and social media posting of job description: $500
Interviewing with multiple people, even a few rounds: $5,000-$10,000
Hring temporary/freelance person to cover work to be done by permanent hire before new employee leaves prior job and starts with yours: $20,000
Filling out paperwork and miscellaneous expenses: $1,500
Employee takes 3 months getting up to speed and not really producing, but still being paid: $30,000
Employee decides the job is not a good fit for him or her and quits 9 months later: $90,000 wasted.
*Total cost to hire and then the person quits:* $184,250 wasted
Additional cost: cost of not getting work done because of hiring errors, that needs to be done: ???? you tell me. A lot.
So a company hires 50 people and 20 quit because the were not vetted propertly: that is $3,685,000 in wasted money. Now, realize that this $3,685,000 is in after tax dollars, so if the company's profit margin is 15%, it takes $24,566,667 in product and/or service sales to cover those wasted hiring expenses. Because those 20 employees were fired or quit, it will take another $24,566,667 in sales to cover the next round of hiring, or almost $50,000,000. If those new 20 hires, if 8 of them quit...well, the game goes on and on.
So, a company best be damn careful in one's hiring practices.
(numbers above might or might not be accurate, but it doesn't matter, that's not the point. The point is that it costs a lot of money to hire and then lose an employee after a short time period due to employee quitting, or getting fired for incompetence, anger issues, harassment problems, or whatever. Hiring highly paid employees is a dangerous game.
This is from the company's perspective, not yours. But if you started your own company, would you want to pay $50 million for bad hiring decisions? No. You would make double-damn sure there would be a lot of vetting processes.
And realize, this is not about you for anyone reading this. It's about the statistics over dozens of hiring decisions.