We were going through a process to make vendor management more standardised and it reached a point where we couldn't even consider adding new vendors.
Adding new services to an existing vendor had minimal paperwork and approvals. As long as you had budget for it, you're unlikely to get any push back.
New vendors required tons of back and forth with legal. Infosec reviews. Additional costboards. Having to justify the vendor to multiple groups. Working out how you get them onboarded into the finance system. Once they're onboarded, we would then have additional paperwork to do periodic reviews to rate the vendor and make sure they're not a critical dependency that will bite us in the ass.
I've only worked with AWS and GCP, but they also throw training and credits at us, too. This could be personalised 2-day classroom events just for our company. There's a huge amount of perceived value for funnelling money through a cloud provider.