How Are Futures/options Standardized With Amount But Stocks Arent?

I heard that exchange-traded derivatives like Futures and Options are traded with a set number in each contract, meaning every options or future contract, you can buy a quantity of 100, no more and no less.
How come stocks and bonds are not the same way? How come there is no pre-set limit to how many you can buy once entering a contract?
PLEASE HELP!!!