Which Dow Futures? YM, DD, DJ?

There are three sizes of Dow contracts. Everyone seems to be trading the YM, so I have a stupid question. Why on earth did they come out with a "jumbo" $25 contract when someone could just as easily buy 5 "YM's".

Or two of the $10 dow contracts.

Why would the CBOT have three products when YM's are enough?

Thanks.

 

Ever heard of commissions?

 

Watch this video for one perspective:

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