Because everyone has perfect sight, wants the same size browser window as the developer, browses at 100% zoom level, with the same fonts, on the same screen resolution, with the same sub-pixel rendering, right? Sure, we're all machines.
Those silly users with their 4K screens should just set them all to 1366x768 like the crappiest notebook LCDs! Jaggies forever! Screw mobile users, damn hipsters can get stuffed.
You're right. Fuck screen readers, accessibility, personalization and anyone with even the slightest disability (colourblind? Sure, we've got burnt umber on light green for you!). Because the designer's view of perfection is what everyone should see, dammit, even if they can't read a word. Design over function.
Of course, if you're being sarcastic, then sure. But you might want to make it more obvious.