[RTTY] Software question

[Bill, W6WRT]

I have a question for the programmers out there. 

I wonder why some programs such as fldigi are written so they will run on almost
any operating system, and others such as N1MM Logger will only run on Windows?

I would love to run N1MM Logger under Linux. Yes, I know about WINE, but
wouldn't it be better if it ran directly? From what I hear, WINE does not work
too well on very complex programs. 

Is it more difficult to write cross-platform software? I know about Java, but I
don't know much.   :-)

All information appreciated.

73, Bill W6WRT