per-minute isn't a crazy unreasonable proxy for it though:
- logs are generally proportional to the length of the job
- other artifacts also usually correlate to an extent
- some of the cost for Github will be for the entire time the job is active: e.g. active connections for log streaming etc. - it's largely correlated to the value the end-user gets out of it
- it's easy to bill for because they can already do billing that way on the hosted runners
- the costs are easy to predict for end-users
It's not like the rest of the Github platform is a per-user cost to run, but that's how Github charge for most features.