I guess you sign up here not to receive bonus exclusively but to keep trading on the platform, make your trading career etc. You can see its fast and easy process to open accounts with different brokers but I don't want to spend time on one of there for a bonus getting frustrated, needing to setup completely new account with other broker. It is just doesn't worth it.
Some brokers as HotForex requires you to trade the number of lot = 2/3 bonus amount, assume you deposit $100 and get $100 bonus (100%), you have to trade at least 75 lot to acquire the bonus amount.