Indicators in MetaTrader returns only values of the indicators. To trade, you need trading logic that is not present in the indicators.
To make the indicators “able to trade” in our software, we added logical rules. So for each indicator, you include you can choose when it should “tell” the program to open or close a position.
According to the movement of the market, those rules get satisfied or not.
If you put your MetaTrader indicator in our software (even if it let you), it does not have any trading rules programmed into it. It could only return points to draw a line on a chart. Since it does not have any trading logic rules programmed into it, you won't be able to use it for automatic trading unless you write those rules into it.
On top of that, we should say here that with the current indicators included in FSB Pro and EA Studio, there is a practically infinite number of possible trading strategies that can be automatically generated and adding one indicator to a field of infinite possibilities won't add much, if anything.
Another reason is that custom indicators are often flawed and might use future data on a backtest that would not be available when trading in real market conditions.
This is why we have limited support for custom indicators.
FSB Pro supports custom indicators in C# (since this is its program's language). If you want to use a custom indicator, you might find it in the Repository or code it.