Most of the time when you get such a bonus there is some hidden information like “You need to trade X number of lots before you can redraw your funds”
This is a little bit tricky because they hold your money. Normally they can’t, if they are regulated. So once you make a redraw they will just take the bonus.
So it is more of a tool to hold you money longer..anyway these are practices of the regulated broker, and these are not Scam brokers.