I'd imagine it's a lot less than "Okay, let's start by going into your dialer settings..."

With fiber, the ISP can see that everything is good up to the GPON terminal. Probably the router too as most customers will just use the ISP provided one. So that leaves the ethernet interface / wifi card as the only thing that would fail and have to be ascertained over the phone, and with a local ISP its probably more cost effective to cut out all the abstractions and just have a tech stop by to check it out.

On the other side, customers have become a lot more used to self help. For example their email isn't even hosted with the ISP any more! I would think that most people would be aware that if a device works good close to the router, and not good far, the issue is wifi range. If they're still calling the ISP, you can direct them towards wifi extenders. Or if device A does not work but device B does, it's not a problem to call the ISP about. And so on.

Of course this is my idyllic view not having worked ISP tech support in a few decades...