You've got it backwards, if an advisor's compensation depended on the performance of client portfolios, they would be incentivized to manage risk very carefully since their interests are aligned with the client's. The only reason advisors do not charge fees on performance is that they want a guaranteed income regardless of the performance of their recommendations which just goes to show that they have no faith in their own advice. It has long been a de facto standard because most clients don't know enough to object and those that do have no other option than to do it themselves. Investment advisors that charge fees based on assets under management rig the system to ensure they get paid whether their clients earn a return or not, that form of compensation is not conducive to a mutually beneficial relationship. The deck is stacked against the client by design.

BTW,C.S. was concerned with an investment advisor, not a financial planner. Financial planners can use a fee-for-service model.