Its how unenforcable all this is. People will come into the fandom, go "oh I have a fun idea" and make it. Perhaps without ever having watched the person in question's content, just seeing them from another PoV. If they're not from mcyt, the idea of looking for a boundaries post will not even occur to them. Even if they are, they might not look (either by being on the fringes, or from CCs who laugh at the idea of making one, or because they are making something they don't want to maintag anyway). Even if they do look, the internet is weird and the list they find may be older and out of date.
Yes everyone is entitled to change what they are comfortable with and discover discomforts etc. But you've got to be realistic about the internet or everyone gets hurt. And right now everyone is getting hurt.
I'd say especially if they come from an RPF fandom there are going to be misunderstandings, because RPF fandoms have existed for decades and the main thing with them is a "we keep to our spaces and you keep to yours", with seperate tags etc. And those are some of the people likely to be most understanding of the fact a creator might be uncomfortable! And most uncomfortable themselves!
(Inspired by recent events but tbh applies much more generally than that)
Also not having a DNI tag (or not saying where you do look) means... Well sure you have 'boundaries' (what they have is a very real thing, but boundaries is not the correct term. Rules, perhaps). But have you ever considered that the fan creators might too? That even if something is perfectly platonic, PG, and canon-aligned the maker might still not want to be perceived?
just gonna comment about the last paragraph because HUGE on that: how are you supposed to know that any art of two characters interacting is supposed to be shipping or not?
most popular ships in fandom come from media that has the characters interacting in ways that at NO POINT were intended to be romantic (see, most shonen mangas, for example); but an audience interprets it as queer subtext
there's no code or rule for what consists of shipping art or not. like sure, clearly sexual or romantic gestures can be counted as shipping art, but what about the characters sat next to each other gazing at the sunset? one could argue it's just an artistic depiction of a canon moment! but maybe the person made the art with shipping in mind, but someone else might see it and accused them of making shipping art simply because it's a "typically romantic scene"
or there's situations like with VSMP, in which there's characters that have relationships that very much might be interpreted as shipping, EVEN when they could also see as simply an attacker with their victim (see, bloodletting)
all in all, it's all a right fucking mess, and it could all be solved if someone acted like an adult, instead of a child who wants things catered for them by outside forces