Bet limitation in Craps

Hi

There is a limitation for number of bets in some on-line casinos during come-out roll. For example: Hardways, Buy, Win (Place), Big 6 and Big 8 bets. Player can't make them on come-out roll or they are marked like "off" and than they don't take part in next roll.
Why this rule exist? Has it any mathematical base or it is just a tradition?

Thanks

I haven't checked each one of these to see, but generally the idea is not to have bets where you would root for "no seven" when the table generally wants to see a seven. It might also be that they just don't want the oddity of players making a bet and instantly declaring them "off" during the come out roll. You might as well wait to place the bet as to do that.

No mathematical basis to this.