Because it's in nominative as subject not accusative as object.

Just like you don´t say "I am eat" in English. You say "I am eating" or "I eat", but there is no progressive tense ( "I am eating" ) in German.

Or herunter?

https://youtu.be/DeumyOzKqgI

I was worried no one got this specific reference ;)

No.

fällt = (he/she/it) falls/is falling
fallen = (to) fall (infinitive) / (we/they) fall

In English-German lessions you will find an onscreen keyboard right below the input field.

In generell see https://en.wikipedia.org/wiki/Diaeresis_(diacritic)#Keyboard_input

Using Mac OS or OS X, a letter with double dots can be produced by pressing ⌥ Option+U, then the letter. This works on English and other keyboards and is documented further in the supplied manuals.

On several operating systems, double-dotted letters can be written by entering Alt codes. On Microsoft Windows keyboard layouts that do not have double dotted characters, one can especially use Windows Alt keycodes.

Character | Windows Code Page Code | CP850 Code

Ä Alt+0196 Alt+142

Ö Alt+0214 Alt+153

Ü Alt+0220 Alt+154

ä Alt+0228 Alt+132

ö Alt+0246 Alt+148

ü Alt+0252 Alt+129

ß Alt+0223