Amazon forking ElasticSearch to keep its old license is a good thing, since ElasticSearch's new license is a proprietary visible-source license. Grafana's new license is still FOSS, so it's really not a fair comparison.
Elastic made a massive blunder by open-sourcing Kibana. SumoLogic just took it and builtnon that. You open-source the underlying technology - not the product built on top of it.
Kibana was open source before they formed the company.
While it is true that Grafana's new license is still FOSS not every company, public cloud provider is willing to accept the AGPLv3 license[1]. Hence a fork with the old license is not unlikely.