Aside from political reasons stated in other answers: Since Article 5 doesn't apply. article 5 states: "The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all [...]" Thist deliberately talks about "armed" attack. Cyber attacks and related aren't covered.

https://www.nato.int/cps/en/natohq/official_texts_17120.htm