The problem is that it is hard to put a size limit after-facts, and the burden that heavy events could create is quite obvious.
This sort of possibility encourage developers to embed images instead of using NIP-96 or Blossom, because it is easier.
And a important and widely used client like Amethyst has a huge network effects in this respect, so with great power should come great responsibility.
I think it's bad supporting markdown in standard note for the same reason, in fact this violates NIP-01 that says:
> Content that must be parsed, such as Markdown and HTML, should not be used.
Please, consider this point of view.