> SCP does not expect text communicating with the ssh login shell. Text transmitted due to the ssh profile (e.g. echo "Welcome" in the .bashrc file) is interpreted as an error message, and a null line (echo "") causes scp to deadlock waiting for the error message to complete.

> As the Secure Copy Protocol implements file transfers only, GUI SCP clients are rare, as implementing it requires additional functionality (directory listing at least).

It points to https://www.openssh.com/txt/release-8.0 for the quote "The scp protocol is outdated, inflexible and not readily fixed."

This comment was related to a security problem last year, https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-6111 . Part of the release notes comments "the scp protocol relies on the remote shell for wildcard expansion, so there is no infallible way for the client's wildcard matching to perfectly reflect the server's. If there is a difference between client and server wildcard expansion, the client may refuse files from the server. For this reason, we have provided a new "-T" flag to scp that disables these client-side checks at the risk of reintroducing the attack described above."

https://en.wikipedia.org/wiki/SSH_File_Transfer_Protocol further comments "SFTP attempts to be more platform-independent than SCP; with SCP, for instance, the expansion of wildcards specified by the client is up to the server, whereas SFTP's design avoids this problem."