Thanks for interesting comments @Joeypark
The reason for this is to use most of the valuable cod as food. In an interesting article in Norwegian, they even named the product from cod heads as a superfood.
See this link for more information:
https://www.sintef.no/siste-nytt/torskehoder-blir-supermat-i-stedet-for-soppel/
The article is in Norwegian, but google translate into English may help you understand the meaning.

Quotation from the headline of this article: «Torskehoder blir supermat i stedet for søppel.
Quotation from the preamble:
«I fjor fisket vi 400 000 tonn norsk torsk. En femtedel av dette enorme volumet utgjør torskehoder, som ofte kastes. Denne "søpla" kan bli høykvalitets proteinpulver.»
In English translation: «Cod heads become superfood instead of garbage»
«Last year we fished 400,000 tonnes of Norwegian cod. A fifth of this huge volume consists of cod heads, which are often thrown out. This "garbage" can be high-quality protein powder.»

Best regards
@Siggjo