The main reason is the lack of value for money. It is not uncommon for them to charge many many more times more than what a discount stock broker would charge.
The main reasons I feel they don’t offer value are:


As you can probably tell. I don’t like full service brokers at all. I see them as legal con artists. For me the only way they can in any way redeem themselves is to move their commission structure over to more performance based structure, instead of a day-light robbery kind of structure.
Of course, they won’t do they, because most of them wouldn’t make any money.
There are high quality discount stock brokers out there charging less than $5 per trade. Full service brokers often charge well in excess of $100 per trade, but at least you get an incompetent pushy salesman for your money.