Yep, IIRC we got 3 months of free prime in 2023. And maybe paid the $1.99 a couple of times. I think what they notice is that you'll order more stuff if you've got Prime and so once in a while they'll offer you a free week or month ( or a $1.99 week). If that's what their algorithm is doing then you should not order anything (or order a lot less) when you don't have Prime and only order from them after you've been offered it for free in order to train their algorithm.