Mojang doesn't look at this website. Suggest it on their Feedback site instead.
Also, I believe the numbers are based from binary code and powers of 2 (like how stacks of items come in 16 and 64, full blocks have 8x8 pixel textures, the world height went through 128>256>320), so 100 doesn't really fit. It could also possibly be as homage to old-school 8-bit games. The reason for selecting "64" as the max stack limit (as opposed to the other powers of 2) is unknown.
Fortunately, there's mods for custom stack sizes/limitations.