Licensed software becomes too expensive, or restrictive licensing conditions.
Costs may be unsupportable, or our use cases no longer supported.
There is very little licensed software still in use in WLCG. The exception is Oracle for services, and Vidyo (60% funded via WLCG). The reliance on Oracle has been reduced significantly over the past years; the license costs are being managed and the need to Oracle licenses at Tier 1s has been reduced to a very low level. Ongoing discussion with ATLAS about remaining such use case.
For Vidyo, there are alternatives now; so competitive tenders should help. For the moment the costs are contained.