If your hiring process can't perform that well, it's broken.
If you have a lot of candidates for example, you may not be able to physically interview them all on the same day (both for your own capacity reasons but also for candidates' own availability reasons for example).
You may think that this does not fit your hiring process. If so, I think you're not really getting what you expect out of it anyway.
As a candidate, I’ve had situations where I got two offers at the same time. BOTH offers were acceptable, both good companies, and I’m confident I would have been happy and successful in either place. With all that being equal, I chose the company that was in my timezone and I had prior connections with. The other company could have done nothing except go waaay above market rate on the role for me.
Some candidates interview just for practice, some are keeping options open, some were solicited to interview and weren’t really looking and the want to get to the offer before they really even begin making a decision.
Likewise, as a hiring manager, I’ve had cases where more than one candidate meets the bar for a single role and I would have been happy to hire either, so “falling back” to the next person isn’t a reduction in standards.
There’s so many reasons that you don’t always hire the first candidate you make an offer too.
This seems idyllic and by your measure every company has a broken process.
Perhaps they are all broken, but which are useful.
As a hiring manager, I’m balancing lots of priorities and hiring is rarely my true #1. When with early startups it’s hard to just logically review all applications within 5 days because rolling reviews are hard.
From an interviewee perspective, I appreciate what you are saying, but typically the interview process for a position could last weeks, depending on the availability of the candidates. Unfortunately, resume embellishment has increased quite a bit over the last decade or two, so candidates who look good on paper aren't great "in the field." This results in an even longer process because you have to manually (via phone call/interview) weed out the embellishers who you thought would be a good fit but weren't quite up to the ability stated in the resume.
Hiring is a slog and it sucks.
If they don't need to fix it, what makes it broken?
I've been critical of hiring in tech for years and years and years, but hiring has only gotten worse (from my point of view) and the companies seem to be fine.
So not actually broken, but someone idealistic or naive or clueless as to the working of a business may think it’s broken.
That is completely unworkable and you will end up with bad candidates or you will have to fire candidates very quickly with a process like that.