Or it's in alpha and they haven't found out yet what the feature is worth to corporate users; so they want to do that before anchoring them to a price.

Also, it might vary per account in an unpredictable way, since it's a heavyweight operation that'd cost more compute-hours when run against larger repos, but also involves static-analysis tasks that don't necessarily scale linearly with LOC. So they might just not yet have a predictive model yet for the baseline cost to them, but instead are doing a trial run for each interested user, observing the cost of the workload on their repo, and then extrapolating that out as the cost to run that workload persistently.

Either way, GitHub has been strongly on the side of "clear pricing" so far, so I doubt they would plan to leave things this way. But it's hard to get enough data for a feature like this, when you know each run you do "just to model the curve" is costing you real money.