Pagerduty: They haven't yet hit that point where PD doubles the prices for them. Or they don't have everyone on the platform, it will be their next Datadog (too expensive)
The insidious part with on-call tooling specifically is that switching costs are higher than almost any other category. Your escalation chains, schedules, integrations with monitoring, incident templates, post-mortem workflows - it all becomes organizational muscle memory. Migrating monitoring backends is a weekend project compared to migrating on-call routing.
What I've seen work: teams that treat on-call routing as a thin layer rather than a platform. If your schedules live in something portable (even a YAML file synced to whatever tool) and your alert routing is OpenTelemetry-native, swapping the actual dispatch tool becomes manageable. The teams that get locked in are the ones who build their entire incident process inside PD's UI.
Anyone implementing PD paging into their company: I highly advise you add a template/interface on top of PD. This will make swapping out later much easier.