It's not the IT admins, it's the CISO or equivalent. At their level they will be concerned with approving anything that's not widely popular and may be perceived as an "unsafe" choice. An extension of the age-old "nobody ever got fired for choosing IBM" line of thinking.
I don't know which companies/CISOs you've worked with but in my experience it's the opposite: CISOs tend to be wary of transferring corp data to 3rd-parties, for both legal/compliance and security reasons. It's generally engineering/IT management that tend to be more wary of self-hosting maintenance.