I have to say what has been said by others before:
Lego is a company.
They are a business.
If it makes money- why do something else? as i said, Lego is a business. and if a theme doesn’t make money for the business, why keep it running? Ninjago has been making money, which is most likely why they’ve kept it going for over a decade. If Lego ninjas make money and Lego pirates don’t, why make would Lego make Lego pirates?