Yes, there is a reason for that.
1. The Outlook Out of Office agent sends the message only once to each person. Especially if, like me, you are away for an extended period due to a sabbatical, I want this to happen with every message. However, this was not a problem for Outlook. I created a flow that does this, and only once a day and per subject, to prevent autoresponder ping-pong.
2. MS Teams does not post the away message but only shows it at the bottom as a pop-up. Experience shows that no one pays attention to it anymore because too many people have entered something there, some of which are also unimportant.
3. The message length in MS Teams is limited to 280 characters. If you want to provide alternative contact options to my teams, this is not enough."