Maybe they saw with some telemetry that very few website actually enable OCSP stampling and decided to implement a fix that cover all certs and can really be deployed
The stapling telemetry is no longer turned on in Release [2], and even if it were, you have to do special things to look at Release data, but some years back (~2018 maybe?) I remember Release stapling was substantially lower than the more tech-savvy Beta and Nightly populations. Which is pretty normal, as tech-oriented sites are more likely to turn on advanced features.
[1] https://telemetry.mozilla.org/new-pipeline/dist.html#!cumula...
[2] "prerelease" https://probes.telemetry.mozilla.org/?search=stapl&view=deta...