I'm confused by you asking why when the answer is both obvious and explicitly stated in parent comments. Sending someone money in a different country, but they happen to use the same currency.
If its within EU there is of course no point in using TransferWise as EUR-EUR transactions are practically free.
In the EU it's nearly always free to transfer funds between the same currency, even between different countries. Banks still get people with the exchange rates or high fees to make transfers between currencies. TransferWise is a UK company, so that being their primary market, they took off from European workers in the UK wanting to send money home.
Just for comparisons sake, my use case is transferring money between Ireland (EUR) and the UK (GBP) and vice versa. Compared to my bank they have both better exchange rates, lower fees, and are quicker.