It strikes me that we are quite often talking about other programming environments which are mostly tied to one dedicated OS.
The reason I went for Xojo is RAD combined with the benefit of not being tied to just one OS anymore. Which "competitive" does offer all that ?
In my case, when I started using Xojo (then Realbasic), my main platform was Windows and I had a lot of interest in Linux. After some bad experience with some PC laptop hardware I migrated to MacBooks and fell in love with OSX. For me the appeal of Windows and Linux is gone. I don't want to even develop for them. So .... for me the two options are Xojo and Xcode. I was experimenting with Swift because it's new and I like to dabble in new languages. But, it is too slow for my use right now (and the ugly implementation of exceptions) so I will be sticking with Xojo.