those extra features are coming at a very high cost, considering that apples is also 6k
If you just look at the pixel count, sure. If you look at the workflow the two monitor enable, you can see the difference. The Apple monitor is a computer monitor - it's quite useless without a computer attached. The Canon does not need a computer and can process multiple input signals on the fly - so users can compare and adjust whatever they need and monitor *while* shooting or broadcasting. Think about broadcaster, who need to ensure a show look good enough on different receiving devices, from 4K HDR ones to older SD ones...
Did you look at the color space supported by both monitors?
About the price, why a 1DX costs $6000 or more, and not $1200 like an entry level FF? Same pixel count, or even lower, sometimes. Or why L lenses cost much more than their non-L counterparts? Why my 24/3.5 TS costs a lot more than the 24/2.8? The latter is faster!!! Why a video camera costs a lot more than a DSLR/ML with video capabilities?
Sure, you can always do an "Harry Film" and buy a consumer TV or PC monitor and hope to achieve the same result at a fraction of the price building some kind of Goldberg machine - you won't, while the system will be much more clumsier and unpredictable to work with.
Apple to oranges comparisons are useless. Apple is not interested in industry-specific devices, just like it doesn't make servers, you aren't going to compare the new MacPro with a Dell heavy duty server - and the latter can even cost more, even when it comes with just a Matrox G200 video card. Still you won't buy the latter unless you really need it. Specific systems for High Frequency Trading can be even crazier and more expensive, and will usually last a few months only. The gains usually offset any cost.