[WouterSpaak]

Typography is a huge part of communication, and by extension, brand identity. Companies value their brand. This is like saying: "why do companies create a whole unique logo for their brand?"

Bear in mind that most quality fonts aren't actually freely available, typography licensing is a complicated maze and for large for-profit companies often wildly expensive. Creating a custom typeface is expensive, sure, but it helps in establishing an identity and it also alleviates huge licensing fees.