I just want to know why they're all written in the most horrible typewriter-style font. They're written on computers now, right? So why not use a font that's easier on the eyes?
But also, the typewriter font is "without personality". It gives a neutral almost engineering feel so you can focus on the content without being swayed by the style of a typeface.
I think it also conveys a sense of technical precision. Every comma, every dash matters. Screenwriting is incredibly precise. In comedy, the exact punctuation is as critical as the words.
(BTW, multicam comedies like Friends are double-spaced and follow a different formatting and speed-per-page. The double-spacing is to allow for handwritten changes and notes.)