I have a couple points for why this just can not happen, and why it shouldn't.
Firstly, progression. It simply wouldn't be fair for some people to progress 'safely' when so many have already done it. Why should you get to do a Tall Tale with no threat to it's completion when others have already done it? Why do you get PL with no threat? You are solo, that is your choice, you can join a Discord and join/find a group just like anyone else. As an additional comment, if there was NO PROGRESSION on PvE, then it can work, but what on earth would be the point?
Second, existing game mechanics simply don't work in a way that supports it. So on a PvE server you pickup a Reapers chest and what, you just get it and never have to fight for it? You want to raise a level V emissary flag and then just have a zero risk 250% bonus while people on PvP servers have to weigh that choice? What about other behavior which doesn't involve actually killing you. I get on your ship and just start throwing your loot overboard, now you can't even kill me to protect yourself. Right now I throw a firebomb on MY ship and it's going to light MY ship on fire, nothing is safe. There would be so much work to determine what PvE even means and it's totally orthogonal to the systems Rare has built.
It's a sandbox game, if you don't like the conditions of the sandbox you need to adjust - leave the server if you see reapers, find a group, go it solo and then accept that is an uphill battle.
Honestly, I go solo all the time and I just don't see the problem, if I don't want to fight, I just make them chase and don't fight. I also accept that if I go on an island for a long time my ship might not be there when I get back.

