The point is, it makes it easy to make mistakes. Somebody might see all of one type of strings, assume that's the format, and forget to enclose the thing in quotes, causing mysterious bugs years later when a differently created date filters into the system. You might have a regex error, you might split incorrectly, you might make a query that works the wrong way and gives an incorrect aggregate, and none of that is due to lack of skill. It's due to not knowing it's the rfc standard, not the iso. It could be due to not even realizing the rfc allows for that or is different.

Software engineering in practice is not about making sure there is at least some way for people to use your library/standard/pattern. It's about making sure the way to do it that's most intuitive/obvious is also foolproof, easy, and efficient. Adding the space makes debugging harder and adds footguns which is exactly what good software engineers want to stay away from. Otherwise we'd all be writing in assembly. But since you aren't, maybe you are the one with a skill issue. Either that or you really misunderstand this field.