They already do: "The loss leaders of the investment world" [1]
Their theory? You'll come in the door for the index ETF and stay for the more expensive funds, the alternative investments, the retirement advice.
[1] http://www.reuters.com/article/us-column-stern-advice-idUSKC...
Seems like that would still be beneficial from a business perspective somehow, although one would probably need to be well versed in banking/finance/securities laws to figure out how to make it so..