PSI4 wants to be nice and provide such a feature, e.g. when you want to reproduce older works.
I wish people would stop using this basis set. The 90s are over, nowadays it causes more harm to the field than good. But that’s my option…
The use of cartesians for 6-31G(d) and spherical for all other Pople ones also lead to more confusion than good. Some programs ignore that and just use spherical functions regardless. Doesn’t matter for at best qualitative results anyway.