Why can I buy a Business Class ticket but not upgrade to Business Class?

Business Class ticket availability and upgrade availability are managed separately. Each flight has a limited number of seats available specifically for upgrades, and these can sell out even when Business Class tickets are still available for sale.

If no upgrade seats are available, you can join the upgrade waitlist if you’re a Finnair Plus member and paying with Avios or upgrade benefits. Alternatively, you can purchase a Business Class ticket directly if tickets are available.