The 'standard' toothpick blade size (maybe 'typical' is a better word) usually is around 4", sometimes a little more, in a handle at 5" or more. Case used to make most or all of theirs about that size, as did most other makers. Case's current toothpick is about 4-1/4" closed, so I'm assuming the blade is probably ~3.5", give or take. Case also has a 'small toothpick' and I think even a 'tiny toothpick' now. I know Queen and Schatt & Morgan still have current models in the 'large' sizes. Eye Brand also, I think.
I suspect most makers are responding to market demands now. Most people won't/can't carry large blades anymore, so I think the 'smaller' versions are a response to that.