Sounds like EVGA looked at the current situation of Nvidia undercutting AiBs with their FE cards, especially during the GPU "shortages".
Also, if the margins are slim and EVGA had made some samples of the 4090, but found the cost to be too much compared to making an actual profit without harming the company and then taking into consideration how Nvidia has been handling the 3000 series, it may have very well looked like a complete loss to EVGA to try and go through another generation with them. If Nvidia is sitting on stock (of the 3000 series) and trying to keep prices up enough on the 3000 series so they can price up the 4000 series (as rumors suggest) coupled with companies having 4000 series sitting in stock, but unable to sell them, that's just money tied up in multiple locations that eats into the coffers.
Lots of "what if" scenarios here and without being on the inside and actually knowing it all, we can only speculate.....
Maybe EVGA made a wise choice to cut ties and walk away? I guess only time will tell.