It's relegated to niche and die-hard users. This is not entirely true. I am not allowed to mention their names but there are a myriad of companies that use PG

It's relegated to niche and die-hard users. This is not entirely true. I am not allowed to mention their names but there are a myriad of companies that use PGP in their software integrations. It is very heavily used for B2B in the financial world. That isn't to say that devs don't shake their fists in anger when trying to do QA testing on software/library matrix of tools that businesses use with PGP, there is plenty of that. On a personal level I have taught many in my circle to use GPG with Thunderbird as it is really just a couple clicks to set it up and no effort to use it. Mozilla did a great job making that easy to use though I have no doubt that prior implementations had soured peoples experiences to the point of not wanting to try it again. Some of your examples are real issues though. Mailing lists are a pseudo-problem in that it doesn't really make sense to use on a public distribution. I've seen it used on Usenet in that fashion long ago but adoption was low for that use case and people complained they could not read the messages not intended for them and that they should use email directly to the people it was intended for instead. What happens when you email more than one person? What entity handles the encryption for each recipient? The email client handles this.