There are three parts to the supplying the data that supports the narrative that I show.

First, often I've had situations where the other party uses the "support it" refutation in some way. In an online environment, the time between the "support it" reply and my response gets responses like "[crickets]" suggesting that the other person won the argument - and that any who see the "support it" being the last post supports the position that I am wrong.

Second, it moves the burden of the previous "support it" refutation to the person without the data and telling a just so story ( https://en.wikipedia.org/wiki/Just-so_story ) or working off of personal anecdotes. A refutation of my post needs data of comparable weight.

Third, sometimes I am wrong. There have certainly been times when I was tracking down the information that would support my position only to find that I was in the wrong. By providing the data up front, I save myself from this possible loss of face from posting an unsubstantiated narrative that runs counter to what the numbers present.