The number one reason is that Grafana is king of the open source operational dashboards. Grafana works with so many backends and has worked so well for so long it’s hard to beat.
Then when you start considering the metric collection and storage setting up a node exporter and black box exporter covers 80% of your use cases. There are scaling and security advantages to Prometheus’ pull architecture too.
I share your annoyance with having to roll out multiple services but I recently bundled them all together into a docker compose that I had been considering sharing publicly. If you can wait a couple weeks I can share that.
One other thought is that separating all of the development of the exporter components means that the teams with real expertise in the service being monitored can collect the best metrics. Rather than a monitoring project making a half ass metric collector for a service they have never used or managed.
Also Grafana has built in alerting so alert manager can be skipped in some cases.
The other advantage of Hugo is that it’s just a single binary executable. Using something like Jekyll means you have to manage a ruby environment over the long term. Which sucks. I’d recommend trying Hugo again and getting past the pain points.