Rare worked closely with Nintendo on their titles. Nintendo provided top-level support for Rare. They had done fantastic with the Donkey Kong Country series on Super Nintendo, so Nintendo had a lot of trust in them and a great working relationship at a time when the company held their cards a little too closely to their chest. I think Nintendo's dev tooling for the N64 was pretty weak and devs were struggling as it was with the transition from 2D to 3D in the crucial early years of the platform. That coupled with the capital intensity made it prohibitive for smaller studios to develop on. But Nintendo trusted Rare and fronted the capital to publish. Later Rare was acquired by Microsoft.