Reason # 1 : For all the reasons quoted by stopthegop :-)
Reason # 2 : No needs to change all the hardware each time you want to use that or this software ;
Reason # 3 : no collusion between the motherboard makers and the main OS developper for constantly rising the needs of the OS to force the users to neverendingly buy new computers several times a year, making them cash fountain ;
Reason # 4 : no needs to wear an armored pants when you go to buy software for it ;-) ;
Reason # 5 : after 22 years I'm still in love and still haven't found better/cooler/smarter computer/OS than my Amigas :-)