I don't think its fair to say FB ads dont work as well when your audience is not ready to buy. If you try to run an Adwords style campaign on FB, then you are right, that isn't very likely to work but that isnt because of FB.
The problem is the ads don't match where the prospects are in the buying cycle. Where FB excels is driving leads into a nurturing campaign that gets them ready for the sale down the line. These campaigns work wonderfully across a wide variety of industries.
If you want to get a better view of this and have Google Analytics conversion tracking setup, you can look at the Attribution reports and Path reports to understand where/how FB and social in general contributes to your conversions.
Google has a decent overview of the high-level topic [1] with a tool to see the change across various verticals/categories, but you can actually calculate a similar chart for your own business quite easily by doing the math on assisted conversions/last click conversions. The higher the number, the more that channel plays a role towards the beginning of the "intent funnel" (defined as awareness >> consideration >> purchase).
Obviously that doesn't mean that channel ALWAYS plays that role (as can be seen in the path reports in GA) but generally speaking, it is not uncommon for display and social to be very high on the assist side of things, and channels like direct, email, paid search, etc. to be stronger on the last touch side. If you discount the value of an early touch channel, you might find that the demand it generates drops off resulting in a loss of volume and/or efficiency for later touch channels.
There are some scenarios where FB and social can drive strong last click performance, but more often it is an assist channel. Being able to measure and manage it as such can easily mean the difference between perceptions of "yes this was a smart investment" vs. "what a waste of cash, FB sucks."
The problem is the ads don't match where the prospects are in the buying cycle. Where FB excels is driving leads into a nurturing campaign that gets them ready for the sale down the line. These campaigns work wonderfully across a wide variety of industries.