There are situations in standard (particularly keyboard) repertoire where the notes either side of a tie don’t technically join up in the middle. The current implementation makes this easy to achieve.
This is the most common sort of scenario where the current behaviour is useful, but it’s not limited to grace notes in the repertoire - this was just the first example I could find quickly:
Further point - pressing T with that implementation could wipe out all or part of the next bar without realising. At least with the current implementation, tie works as expected, and no extra rhythmic values are created (which could be confusing)
But in your example there must have been a note to tie to - Dorico won’t produce ties to nowhere. (There’s separate l.v. tie functionality that handles that.)
Maybe a better approach would be for dorico to warn user that there are no notes after the first selected notes and stop the user from pressing the “T” button so we won’t have issues like this.
I don’t remember now, but I think that is what happened in Sibelius. When I pressed “T” button and there was nothing to tie it to, It simply canceled the Tie shortcut.
As I just said, there are notes further along the flow for Dorico to tie to, even if they’re outside of the area you’ve chosen to screenshot. If they didn’t exist, Dorico wouldn’t produce ties at all.