SQL isn't necessarily something published to the web and many SQL systems lack the easy to use easy to create Interface system like FileMaker. Thus, you may want filemaker because it is easy to develp with and familiar to the developer.
Also, you may be transitioning from an all filemaker solution to scaled up SQL system and this can enable you to keep the existing and familiar interface intact when making such a change.
Thank you Phil, that makes sense. I still say the times I would mix these two technologies are very rare and limited, but thank you for giving me an example of why someone would even want to do that in the first place. You made some good points...