Why is it das Aussehen?

Aussehen is the verb aussehen used as a noun, and verbs used as nouns are always neuter: das Aussehen.

More verbs used as nouns
Sense 1
das

Meaning

[1] A sight that someone else offers

[1] Anblick, den jemand anderen bietet

Examples

[1] Its appearance is a deterrent for most people.

[1] Sein Aussehen schreckt die meisten Leute ab.

[1] She is a wealthy woman by appearance

[1] Ihrem Aussehen nach ist sie eine wohlhabende Frau.
More source examples (4)

These dictionary examples can include historical and less common uses.

[1] People shouldn't be judged by their looks

[1] Man sollte die Menschen nicht nach dem Aussehen beurteilen.

[1] “For men, appearance is of secondary importance” [1]

[1] „Bei Männern ist Aussehen zweitrangig.“[1]

[1] “So even these rag brothers were careful about their appearance” [2]

[1] „Sogar diese Lumpenbrüder waren also auf ihr Aussehen bedacht.“[2]

[1] "My appearance prompted you to ask whether I was sick?" [3]

[1] „Mein Aussehen veranlaßte sie sofort zu der Frage, ob ich krank sei.“[3]

Declension

1 Singular Plural
Nominativ das Aussehen —
Genitiv des Aussehens —
Dativ dem Aussehen —
Akkusativ das Aussehen —

Pronunciation

Dictionary entries include material from Wiktionary. Wiktionary