"... but that would mean management admitting they made a mistake."
Bingo. Some of ours will swallow all of the marketing bilge they're given, and a lot of that is second-hand evangelising by our own managers who have already swallowed it themselves.
When things go wrong or performance suffers and staff start to complain, management explain the service is cheaper... constantly updated... new features all the time... etc, whereas had the same issues occurred when on-prem, those same managers would have been pointing the fingers and demanding action as IT were not providing the service the should.