Delphi was so powerful when Win32 rich clients were king. Pre 1998 the web was not a serious development target for applications for most people. Mac OS was on a pretty large downward spiral. Linux was still under the radar (and changing too rapidly for serious closed source development).
But the web started developing, OS X started to win back the crowd and Linux showed potential (I stopped doing Delphi development when I moved to a linux box).
Since then they have added a lot of the functionality to do cross development, however a lot of it was too late, and worse a lot of it is ugly. I have never found a rich client building experience as good as Delphi. I still think it is one of the best IDE / GUI Builders packages ever assembled. However when I went for a look back at in a few years ago, the price was eye watering, and unfortunately it seems if I want that style of development my best bet now is C#.
A pet theory for why OSX and the web seems to be such friendly is that the early web was considered an extension of print (and later video/audio) media.
And as best i can tell, media production has been long held bastion of Apple.
It likely didn't hurt that OSX is deep down a BSD, and so you could switch out the L in LAMP and be on your way.
Certainly media companies have always worked on Macs, but the platform was actually quite bad for web development in the early days. The colors were wrong, the fonts were wrong, the entire scaling was wrong. Mac users had a defective version of Netscape and a uniquely defective version of IE.
It wasn't until Mac browsers adopted "standards" which matched the Windows way of doing things (96dpi, sRGB, MS fonts) that the Mac was really a viable web development platform.
But the web started developing, OS X started to win back the crowd and Linux showed potential (I stopped doing Delphi development when I moved to a linux box).
Since then they have added a lot of the functionality to do cross development, however a lot of it was too late, and worse a lot of it is ugly. I have never found a rich client building experience as good as Delphi. I still think it is one of the best IDE / GUI Builders packages ever assembled. However when I went for a look back at in a few years ago, the price was eye watering, and unfortunately it seems if I want that style of development my best bet now is C#.