Microsoft is serious because the world is full of people with needs who do not know better and Microsoft is still the default to serve those needs.
Something does not have to be useful, benign, consistent, worthwhile, or deserving to exist in order to be serious.
For example: Losing an arm and an eye to a fireworks accident, being grievously assaulted in an alley, or having Microsoft arbitrarily delete all your data, are all very serious things. So, I think it is fair to say Microsoft can still be called serious.
Something does not have to be useful, benign, consistent, worthwhile, or deserving to exist in order to be serious.
For example: Losing an arm and an eye to a fireworks accident, being grievously assaulted in an alley, or having Microsoft arbitrarily delete all your data, are all very serious things. So, I think it is fair to say Microsoft can still be called serious.