The price? It costs around $300 for Canon. The question is not if the Canon cine CN-E 85 is better. The question is: does it include $4700 worth of improvements over the Samyang?
That's the difference between a cheapskate and a smart person. A smart person spends the money, no matter how much, when it's the only option. A smart person will also spend the bigger amount when the benefits justify the extra cost. A cheapskate will always choose the cheap option. A smart person will not, however, spend a very much larger amount of money for minor improvements, when the improvements don't justify the cost, aren't required to get the job done, and when the extra money could be used for other lenses/equipment.
I'll jump into the fray here because I think you are missing a number of points. There's more to lenses than image quality and test charts. Let's compare another lens the Rokinon/Samyang/Bower (et al) 24mm 1.4 vs. the Canon 24 1.4 II:
Canon, yes; Rokinon, no
Tough construction (won't break on a paying shoot - I've dropped my 24L on concrete with no issues):
Canon, yes; Rokinon, decent, but not tough
Canon, yes, multiple US service centers, Canon Professional Services; Rokinon, no US support
Autofocus (we don't all shoot landscapes and buildings with 24mm lenses):
Canon, yes; Rokinon, no
Image quality @ f/1.4 (http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=480&Camera=453&Sample=0&FLI=0&API=0&LensComp=821&CameraComp=0&FLIComp=0&APIComp=0
Canon, good, useable; Rokinon, soft, lots of CA
Canon, well-corrected; Rokinon, not so much
Canon, abysmal; Rokinon, better, but still terrible
Canon, slight, small artifacts; Rokinon, slight, large artifacts
Conclusion, Rokinon saves you about $1000 ($669 vs. 1668 currently). That's great unless you want to shoot wide open, shoot something moving quickly, go out in bad weather, or in conditions where the lens might get bumped or broken. If it breaks, you pretty much have to buy another one. Now you're only saving $330.
You can either buy right once, or buy cheap, buy cheap again, then buy right. Read Thom Hogan's tripod article for reference: http://bythom.com/support.htm
Back to the original topic, the 85 1.8 and 1.2 are two totally different lenses and really shouldn't be compared for anything other than portraits. The 1.8 is a nice lens and is better at nearly everything else, but the 1.2 is clearly the best portrait lens. For some it's worth the extra money for the seemingly small gains (or not so small as neuro's sample's show), for others, the 1.8 is more than sufficient. The 1.8 in a talented photographer's hands will beat the 1.2 in a rookie's hands, but give that same person a 1.2 and they will never want to go back to the 1.8, at least for portraits.