You might have implemented the t-string to save the value or log it better or something and not even have thought to check or escape anything and definitely not everything (just how people forget to do that elsewhere).
class DB:
def execute(query: Template):
...
db.execute("QUERY WHERE name = ?", (name,))
db.execute(t"QUERY WHERE name = {name}")
Just because templates (or the previous syntax of passing in variables separately) could be used in a way that's equivalent safety-wise to an f-string by a poorly designed library does not mean that they add nothing over an f-string in general - they move the interpolation into db.execute where it can do its own sanitization and, realistically, sqlite3 and other libraries explicitly updated to take these will use it to do proper sanitization.
You're right that the authors of such libraries could choose to do something different with the template parameter. But none of them will, for normal interface design reasons.
A library author could also write an implementation of a `plus` function on a numerical type that takes another numerical type, and return a string with the two numbers concatenated, rather than adding them together.
But nobody will do that, because libraries with extremely surprising behavior like that won't get used by anybody, and library authors don't want to write useless libraries. This is the same.