No shit the VMU as it was isn’t capable of MP3 capabilities. Not sure how crazy tech advanced you think mp3 players were in the beginning, the simplest mp3 players didn’t even have a screen, they were plug n play with direct drop file library- no software required and ran on a single AA battery. Also not sure why you think the disc reader wasn’t fast enough. Most people were happy to spend 2-3 hours ripping and burning a music disc. I think you’re comparing it to modern day expectations.
The Dreamcast came out in time where people were happy with any tech that was dual purpose and any that was cable of multiple functions received huge attention.
Here’s Sega’s VMU Mp3 player prototype: not saying this specific one would have been the one, just saying it’s capable.
https://www.thedreamcastjunkyard.co.uk/2016/10/a-closer-look-at-dreamcast-mp3-player.html?m=1
Tires also used to last longer. They are designed to wear out faster now.