The recent ESMA regulations require that brokers operating in their jurisdiction must show on their websites the failure rate of their clients. Currently, these seem to all reflect a failure rate of about 80%
As for the reasons, if you put “fail” in the search function you will find lots of threads full of suggestions why this is. This is obviously an issue that concerns many traders and therefore this question has been asked many times before.
Read, learn, and avoid! Good luck!