I have read the Wiki and FAQ; (UA asserts that the Earth is accelerating 'upward' at a constant rate of 9.8m/s^2)

But am struggling to find either a reason why or proof that the earth IS accelerating at 9.8 metres per second:

Wiki states: "The are several explanations for UA. As it is difficult for proponents of Flat Earth Theory to obtain grant money for scientific research, it is nigh on impossible to determine which of these theories is correct."

I was hoping that a FE could explain why this theory exists without this reasoning and evidence? Why does it make sense to you and how did this exact speed come about? As for the several explanations for UA; what are they please as I could not see t
many thanks