It's like you don't remember E3 flash sales, holiday sales + every so often got big discount. The game was on top during these months due to that. No need to be an insider, just observe Amazon and NPD threads.
If you just wanna point me as a downer, then do so. Fact is the game sold really well. Fact also is that legs are also due to heavy discounts and bundling.
as we can read from your first stanza, this is your personal interpretation/deduction of the games sales' pattern, which means that in fact it's not a "fact", but a relatively educated guess
presenting your deductions as fact imo is bad manners, as it's sure to lead to unfruitfull arguments