Because it can also hurt you to have too many cards open (if not on your credit report, then with a particular bank).

In other words, when taken to the point of opening multiple cards every year, you can't possibly leave all of them open, so you have to close some to make room for newer ones. Every churner after signup bonus points with multiple programs is familiar with this.

I've been doing such churning for well over a decade, and my score is still above 800, thought not quite as high as yours (but the main complaint that I see below my score is not about how many cards i closed, but about not having recent installment loans. So I'm "dinged" on credit because I buy reliable cars that run perfectly for years after being paid off, and because I rent instead of owning a home. I do have several cards that I've had for more than a decade (Discover over two decades, Citi AT&T Universal over two decade), and I don't feel I need any more. I "naturally" occasionally find no-annual-fee cards (or "net negative annual fee" cards, as with several Chase hotel cards) that make no sense to get rid of and that i actually use, that I don't see the point of taking yet more cards and converting them to something I'll never use. It's only my couple two-decades-old cards that I keep whether i have much use for them or not.