Why are cassette and CD players so bulky now?

From what I understand there is only one manufacturer still making cassette mechanisms and all the current players in the market have no choice. Those smaller sleek Sony units were no doubt optimized in house manufactured units.

The market disappeared, that's why, just because the market is starting to come back in a small way doesn't mean the people that ran those factories making those things from decades ago want, or can, make them again.