Except that most investors can't read/understand the menu. For many (read: most) it's like trying to read a menu in a foreign language while you suffer from a severe peanut allergy.

In choosing your advisor you can select someone who is fluent in both your native and the foreign language (product specialists), someone who understands your dietary needs and aversions (asset & risk consultants, quants), or someone who considers both aspects of your situation.

As for clients wanting to "win big", you're right, however where it is likely to be at detriment to the client it can nearly always be overcome through discussion and explanation of the risk factors. If they reject this advice then it's likely to be a difficult (or at least not a satisfying) relationship. In this case we will not accept them as a client.