Why does Excel saves a template with macro (XLTM) as a normal Excel file (XLSX)

When I prepare a file with macro's (to be used by other people), I save this file as a template with macro's with the extension *.xltm (template with macro).
Therefore no one can overwrite my file.

These other people can open this template (e.g. double-click, but not file-open).

But ............. when these people save this file, Excel automatically saves it as a normal Excel-file with the extension *.xlsx.
Ok, a message is seen after pressing <enter> or clicking Save, but does normal users know, what they have to do then?

If I'm making a template with macro's, I want Excel to have this file saved as a file with macro's.
Whatever did I make a file with macro's for?

Is this a bug or is it done on purpose?

Thnx in advance for any reaction.