Why did the dealer ignore my Car Guru's offer?

Ask them. My guess is that they are car dealers (not a compliment).

Dealers are not required to accept any offer if they don't want to. Especially if they have another interested person. Back in November I was looking at a 95 BMW. I had the car inspected and, not surprisingly, it had a few issues. The Dealer wanted $3,500. For it. I offered $2,000. They declined my offer and made a counter offer of $2,995. I said no, $2,500 was as high as I would go. The Dealer declined and a few days later the car sold. They obviously had another person who wanted the car and was willing to pay more than me. Hope that helps! Jim