digested by the engine
The reed moves, or flexes, on every intake/exhaust cycle. ALL materials, be they metal, or that new fangled carbon fiber, "fatigue", meaning they have a cycle life, so many "flexes", and they break up/off, and are sucked into the engine. Now you have shrapnel, of one sort, or another, flying about inside your engine, making short work of the bearings. The claim that a carbon fiber reed does not bother anything when it gets sucked in is false, the damage is less, but there is still damage.
A 2 stroke engine has 3 methods of induction: piston port, reed, or disk valve. The advantages to reed induction are: low cost (higher than piston port, lower than disk valve), and a longer induction time than piston port (giving better performance than piston port induction). So generally it gives the best performance for a reasonable cost. Reed valves are a regular service item.
There are some situations that reed valves are not suitable, one is a supercharged/turbocharged situation (2 cycle diesel), where the positive pressure in the intake will hold them open.