iPods were great for DJs in a way that smartphones haven't been able to mimic.
You could just put like 40gb worth of music on there, and then play it on almost any sound system of the time (without an internet connection!). Output via audio jack or USB. And, crucially, iPods had no notifications, ever, interrupting your music. They never needed to have their software updated, either. Like, there were bugfixes and stuff, but you could ignore it and they worked fine out of the box.