Google certainly could charge a very small fee for existing gmail, youtube, etc, accounts and make a bunch of money.

In fact there is a pretty strong argument that they are leaving money on the table by not doing so.

Imagine you like your gmail and you have had it for the past decade. If Google charges only $1 per year across say a billion users that is a billion dollars.

Even if they lose some users at the margin it may makes sense...

According to wikipedia gmail had 1.5 billion active users in 2019.

As internet services mature and stop growing exponentially it makes sense to charge for them.

Yes it is true that some might switch but what makes more sense from the perspective of most users?

While I agree with your premise, once you charge someone for something, even if it is $1/year, then they start expecting something for that money above and beyond what you provided earlier. In other words, now you've got to budget for real customer support and that will undoubtedly cost you more than the $1/year you're receiving as payment from that customer.

$1 a year would probably barely cover the administrative and payment processing costs. $2 a year would do the trick though. :)

Charge for the service and show you ads and sell your data like cable. It’s a win, win, win!

I long for a post advertising world. What cataclysmic event or human evolutionary change could cause that, I wonder.

Is there any sci-fi that has a world without advertising or is that so far-fetched it’s unimaginable to even futurists?

Funny enough advertising was relatively small part of the economy until the last several decades. Now it is an "industry" in the multi-trillion dollar range.

Even funnier, if Google search worked effectively for product discovery the vast majority of advertising would not be necessary.

Good point. Maybe the death of advertising comes when some entity knows us so perfectly well it automagically provides the exact thing we want/need exactly when we want/need it.

Google used to for me at least from around 2010-2015 +/- a few years. It was incredible. Now it is usually very hard to find anything I want via search. I suppose a certain amount of defect in search results is optimal for the ad business.