Because it's a very rare and precious individual who managed to increase their flying in 2020 over 2019, or indeed over any representative year in their recent past!

However, as I'm sure you well know, my advice to the OP back in April was intended as being that s/he should NOT acquire a credit card for the purpose of the few XPs it brings, if they couldn't then reach the Gold status threshold by acquiring the relevant number of additional XPs by other means, i.e. flying. As you will see, my response was to specific comment in which the poster to whom I replied indicated an assumption that reaching Gold was the entire focus of this question. If the OP's true goal was indeed to reach Gold, and given that they were very concerned about just how many XPs they could get by not flying, you will see that it is not so unusual to already detect a reluctance on the part of the OP to actually accumulate many/any XPs by actually flying. On the basis of the OP's apparent location, and the fact that the subsequent doubling of XPs offered in FB does not apply to Delta flights, the OP would have been required to do at least 16 domestic sectors, even after "maxing" out their credit card spend.