Lowercase "in" is a major part of their branding. Forcing usage of lowercase "in" in this scenario supports the branding even if it doesn't make sense from an engineering standpoint.
They can redirect from the upper to the lower case URL so that it still looks the way they want.
It might not be intentional that it doesn’t work with uppercase, but they just made it lower case and by default it’s case sensitive on whatever software stack they use to host.
