how do I accept I'll never know why any employer rejected me?
I'm finding the hard way that finding another job is a grind: you invest time reading what they want to hire, you write a CV and an application.
Most of the time you don't get an answer, meaning you are that irrelevant to them. Most of these times it is YOU the one who has to ask if they decided for or against. On the limited times they write you back, it's a computed generated BS polite rejection letter.
I asked one of them how many candidates they considered and why they rejected me, but that only made them send me another computer generated letter.
I'd like to know how close I was and in what ways I can become a more interesting candidate, but nobody is going to give me a realistic answer.
It sucks having to need them more than they need you. And I should consider me lucky, because I have a job, but jesus christ, I feel for those who have to do this without stable income or a family that offers them a place to stay...
Don't take it personally, applying for a job is a game of chance as much as a game of merits. It's simply a numbers game and luck whether your resume even gets looked at in the first place, even if you're résumé how all their keywords. Hundreds, maybe thousands, of other resumes also hit their keywords.
If you're lucky enough to get through the first sifting and get an interview with the hiring person (not an HR screener who doesn't know anything about the job), then you can ask and maybe get a response on how you could have improved. (Don't ask why you weren't hired.)