Because people who trade stock prefer it that way.<p>You&#x27;re free to setup a market that works in this way, and if consumers prefer it you&#x27;ll make millions.<p>I&#x27;d hazard a guess because the point of markets is to disseminate information and the point of diplomacy is to keep information secret.<p>Seriously, look at it like this, this buyer is a big smart human with a big brain that talks to other humans and likely knows &#x27;secret&#x27; information about the company, lets say it&#x27;s Wal-Mart and he&#x27;s ordered satelite photos, etc to gauge traffic and knows they are doing well. He has all that information and all the algo knows is &#x27;BUY 20000 @ $4.53&#x27; the algo disseminates that information to all the other traders by cancelling its quotes.<p>The buyer pays a premium to gain 83% of the available stock on the market. It&#x27;s like Mark Cuban and his Yahoo stock, if he dumped it all the day he got it the market would tank because there&#x27;s more supply than anyone wants, so he wisely instructed his broker to sell over a longer period of time. The buyer could have chose to do this, or he could attempt to buy 83% of the available stock all at once in hopes no one noticed.