iTunes is here because Apple hasn't released a Linux version, so all
of us Linux users that want iTunes need to run it through CrossOver.
QFT
I hope the OP is truly confused and not just feigning ignorance just to pass off flame bait as a legit question.
As far as I know Apple hasn't released iTunes for Linux. And no, people who have Linux run machines and prefer Linux run machines can't just push a button and have it magically transform into a Mac Pro thereby satisfying the question why we can't just use iTunes for Mac OS X. There's a reason why we choose Linux over Windows or Mac OS X. And to use iTunes for Windows we'd either have to dual boot and boot into Windows whenever we just wanted to listen to music just then, or use virtualization software which has its own problems with compatibility. I tried iTunes Windows in XP in Parallels. The cover flow function wouldn't work. Music played, but video was choppy and stalled. The only way to use iTunes fully right now is to use it under native running Windows XP or to buy a real Mac and use iTunes there (and we all know what the answer from the Mac cult would be to that).
Miro almost does it with the podcasting, but it's "auto resume playback" feature breaks after using it for a while. And podcasting is the last feature that I'm really picky about. In iTunes you can auto resume and I liked that. In players like Rhythmbox which have a podcasting feature most player like that don't have the crucial "auto resume playback" feature that I think is a must must must in order for it to be a competent podcast client. Miro is the only player that has that and it breaks. :(