The term financial advisor is a broad term and not all financial advisors sell insurance. Although, yes man financial advisors are primarily selling insurance, mixed in with some mutual funds. The insurance policies are their main source of income.
Also be aware that there are fiduciary and non fiduciary financial planners. If they are a fiduciary, they are required to act in your best interests, even if it contradicts their best interests.
Fee structures vary, but basically there are three types:
1. Fee only (advisory fee)
2. Commissions
3. Combination of fees and commissions for fee based
The fee only structure offers the most transparency. You know up front how much every transaction costs and how your advisor gets paid. This can be one issue with insurance is the heavy sales commissions and fees that are not transparently disclosed. Try asking a financial planner on Bigger Pockets to disclose their commission and they just say things like "everyone deserves to make a living".
My parents have a financial planner that charges a percentage of assets under management. He is not compensated for transactions, so he has no motivation to buy and sell investments or sell insurance. His only goal is growing their assets.
I personally fired my financial planner after the 2008 crash. Not because I blamed him, but because I realized he was doing nothing besides collecting commissions. I switched to low fee index funds, a couple individual stocks and self manage real estate.
The dirty little secret of the financial industry is that fees destroy returns. Heck, I would even argue this is true of real estate when hiring a property manager. If you are paying 3-5% on management fees and the market returns 7-8% on average, you can see how much the fees erode your investment. Same for property management, if you are paying 10% off the top, and hoping to get 15-20% return.
Studies show that it is rare for financial planners to beat the market with active management. Why pay someone to perform worse than the market?