This has been discussed elsewhere. Scintilla supports multi-paste into multiple selections, but it is a choice, both single and multiple paste are useful in that situation. The paste command infers the answer from what is on the clipboard, if its a single thing it pastes single and if its a multiple thing it pastes multiple.
If the contents of the clipboard is a single entity the paste command cannot read the users mind and decide if they want to paste single or multiple. A separate command is needed (or an option but that is considered to be less user friendly) for the other choice. Pull requests are welcome.