To begin with, Buy-Side and Sell-Side are not exactly what they seem. Let us start with some definitions, from Investopedia:
The side of Wall Street comprising the investing institutions such as , pension funds and insurance firms that tend to buy large portions of securities for money-management purposes.
Read more: http://www.investopedia.com/terms/b/buyside.asp
The retail brokers and research departments that sell securities and make recommendations for brokerage firms' .
If both buy and sell decisions are enabled by these Sell-Side analysts, why call them only Sell-Side?