My process had over a dozen stages, mostly 1+ hour video calls, one of them a 2-hour tech test. It took several months to complete.
I wasn't in a rush (I actually walked away from it for about a month in the middle for personal reasons), and they were being a little cagey perhaps because it was a senior-ish hire into tech (Principal), and picking the wrong person at that level can do serious damage to a tech culture. I appreciated they took it that seriously.
They then were prepared to wait for my notice on my existing role, which was 3 months (negotiated down to half that in the end).
That shows commitment on both sides.
This is going to be a stronger trend. There are a lot of people out there with a CV that says "senior developer" on it, asking for top-drawer contractor rates, feeling a little entitled because they know some React or Go, so it makes sense to take your time and really, really kick the tires.
With a remote workforce, able to hire anybody in any country, it makes sense to really find the best you can: they can make or break your business. Makes sense to me.
There is research - but I can't place where/when I read it right now - that says you should decide how many people you're prepared to interview, then discard your first third of that number. Then hire the first person you meet who is better than the best candidate in the first third.
I agree that hiring someone wrong can be damaging, but you can usually screen out obvious incompetence pretty quickly for any level real fast in onsites.
If I was the candidate I would assume they have a culture of waiting for perfection before shipping tomorrow rather than shipping something OK today and that is not the culture I want to be a part of.
Please note that I'm only detailing what I personally would infer from their decision. They may very well have a totally different culture.