You only need to roll a dice 99 times to get a 256-bit number. Which gives you a bitcoin private key.
Given that 4 out of the 6 results add 2 bits and 2 out of the 6 results add 1 bit, then each dice roll gives on average ~1.66 bits. That's 256/1.66 = ~154 times. But, there's no reason to do this for a bitcoin private key and not for a seed, which will then generate infinite keys.
You only need to roll a dice 99 times to get a 256-bit number. Which gives you a bitcoin private key.