Having a Service Desk that actually provides usable and composable tooling is a benefit for all. Having a random contractor "implement" ServiceNow because Gartner said so is a pain for all. This is of course a bit of opposing extremes, but the same applies to JIRA and AD and pretty much anything else. Hard-pushed bad implementation will ruin your workday.
Teams that are capable and allowed to self-steer and deviate from company policy if they come up with a good enough reason seems to be the sweet spot of attainable & realistic.
We dropped SN a couple years back over this. They were charging us about 6-7x what we pay for Jira, and we still use the on-site enterprise version of Jira.
Usually, if it isn't better from a staff-perspective or better for the customer, self-hosting or self-building is less likely to be the answer these days.
My guess is it's because Jira actively targets SMB, while ServiceNow is almost strictly enterprise, and folks in enterprise have already resigned to their fate.