As someone who was advised to wait 6-12 months for a tax refund in Finland (not a standard payroll/prepaid tax) [1] I'd say it's because 'the system' is still the old system from the past that hasn't entirely kept up with the fact that in this day and age:

- A limited company is not always a giant manufacturing concern

- An ever increasing amount of the population will not have been born in and will not be living their whole lives in Finland.

IT is a nice frontend for it and can serve you in many languages and with the latest and greatest UX - but the actual processes and decisions are not keeping pace. Changing these is a high-friction, low-reward endeavour for politicians.

[1] https://www.vero.fi/en/About-us/contact-us/processing-times-...