Keeping the Auditors happy
Knowing that “everyone does it” - the vendor told them so
Bragging rights (expensive hardware)
Being unbothered by fighting with facilities for building penetrations and antenna mounts
Misunderstanding the beauty and economy Dave Mills marvelous algorithms for consistent time based on multiple sources, even those connected via internet
Unwillingness or inability to leverage other local resources capacity to run ntpd with minimal impact in order to have a good constellation of local NTP servers
Willingness to farm out time service without doing a deep dive into why and how, just leaving the design to the appliance vendors

This covers most of what I have encountered in providing enterprise time services for $dayjob+clients. I probably left out some significant points, but it has been a few years...