I think I can offer a reasonably informed explanation.
New Relic Logs and New Relic Dashboards are two distinct products. Logs is the relative new kid on the block. Whereas New Relic has offered some variation on Dashboards for many years now, with the previous incarnation being known as Insights.
When creating Insights, we needed a query language that was fast, flexible, and easy to learn. Thus NRQL was born, and for some time was the only way to query data in New Relic.
Since the launch of New Relic One we have dramatically expanded our product offerings, ingesting new data types we’d never had the ability to accept before. With these new offerings came new ways of looking at the data. Some of these were new to us, and some, such as the Kubernetes Cluster Explorer, were new to the world.
When it came to logs, we sought to offer a familiar way of viewing and searching logs for users that had spent time using other log management tools. From this effort, the Logs UI was born. We chose to use Lucene as the query language for Logs as this was already a popular query language used by other well known log viewers.
At the same time, we wanted to expose the data found in logs in a way that allowed users to slice and dice their log data in a myriad of ways that traditional log viewers couldn’t offer. The obvious answer there was to leverage the technology we already had in NRDB. Storing log data in NRDB makes it available for querying in Dashboards and Insights, meaning the function and convenience of NRQL can be applied to the attributes found in log data.
To sum it up, I’d say that the Logs UI offers a way to view log data that allows users familiar with other log viewers to get started quickly, without first needing to learn a new query syntax. While the ability to query log data using NRQL opens up a range of use cases that traditional log viewers are unable to offer.
To be clear, this is my opinion based solely on personal observation, and should not be considered official documentation.