Conditional SSI (if/"elif"/else/endif as well as if/else/endif variables)

Does anyone know why this is supposed to be a feature as far as I'm aware of more recent versions of apache yet dosent seem to be enabled in most linux web server setups, or is it usually turned off due to performance impact concerns?

There are a couple of instances where I could really use it but no matter how I try I just get errors all the time.

More functions to SSI more security risk.
You already can read most of the files with SSI.

Even when the likes of exec command can be used yet SSI else if command cannot, that dosent strike me as balanced somehow?