I can't help but agree. This is such an odd design decision.
I've been working on a few flows and wanted to try out a few possibilities to make things smoother. I even went so far as to design an adaptive card to make my message neat and professional looking.
Instead, it quite neatly drops this message between the test of the message and the action (URL) button. The makes some sort of sense in that the action should be at the bottom of the card. But now I have no way to make a professional-looking card because there is an ugly blob of advertising text right in the middle.
Really poor form Microsoft. I for one am simply going to abandon this idea for now, which is a real shame considering the potential benefits this could provide.