They aren't regular tokens. Each crypto-kitty has an other value.
If one bitcoin has a value of $1000, another bitcoin is also worth $1000. However, Crypto-kitties do not work like that.
Some crypto-kitties are bought for a couple dollars, whilst other crypto-kitties are valued at multiple Eth.
Therefore, available supply is useless. If they're all the same, that works, but not if they're all different.
To be honest, I don't invest in Crypto-Kitties, purely because I know it was(and is) a bubble, which sadly, is unsustainable and very unpredictable, making it very risky to invest in it.
Unlike Bitcoin & other cryptocurrencies, it doesn't really have a use, other than buying & reselling either.