@xtof That is set by Mastodon so there is no problem with federating for remote instances.
If every instance could upload whatever file sizes and types they wanted, that could open up a bunch of problems for the remote instances that could not deal with those formats or don't want to host those files (every file you post is copied to the remote instances where you have followers).
It's something that you can bring to the Mastodon team, either https://discourse.joinmastodon.org/ or in Mastodon GitHub.
Mastodon é uma rede social baseada em protocolos abertos da web e software livre e gratuito. É descentralizado como e-mail.