Why did "one" as a pronoun drop out of use?

[saje]

@BigT

This is relatively easy to avoid. For example, what you are actually saying in you final sentence is that “it would be nice if I could say what I thought without having to add [a disclaimer].” Or possibly “it would be nice if everyone could say what they thought without having to add [a disclaimer].” Or even “it would be nice if people could say what they thought without having to add [a disclaimer].” All of these work fine.

Examples from a website explaining the use of “one”:
[ul]
[li]“One would think the airlines would have to close down.” Clearly a statement of what the speaker thinks, so easily replaced with “I.”[/li][li]“The young comedian was awful; one felt embarrased for him.” “I” would work here, too, but a better replacement would be “everyone.”[/li][li]“If one fails, then one must try harder next time.” “One” is actually horrible here, since it could refer to a number. While “you” would be the most natural replacement, since we are dealing with an aphorism, “someone/they” works well enough.[/li][/ul]

That website says that the replacement with “you” is an American thing. Is the use of “one” as an informal general pronoun that much more common in British or International English?

The context I’m thinking of is well, here:

@saje

I think that if you (a generic you) are going to come in close proximity to something frequently in life that you are concerned about, it would behoove you to learn something about it. If you live in an area where lots of people have dogs, or you walk in a park that has play areas for dogs than it’s to your own benefit to be able to spot problems before they happen, and not cause problems inadvertently yourself.
…

This is from a somewhat contentious topic in the Pit. I wanted to make a point using one person’s quote, but I didn’t want to attack that person specifically, just use their quote as a handy reference to what several people were saying.