I think there is probably less of a technical answer to that. And more of a Mozilla policy answer.
Trust stores have certain rules about how you can get your root CAs into and out of it.
Mozilla also has such rules. I don't completely understand them.
But the general idea is that once your root is inside the Mozilla trust store the regular way you can get thrown out is via a two step process: first your root is left in the trust store, but placed in "deprecated" status. And after your root has been in deprecated status you may then be thrown out completely.
If on the other hand you already have a root CA in the Mozilla trust store and only want to renew it, then the rules are slightly different than if you had no root CAs there. (Not sure about that part.) They have a special section on the wiki named Requests from Already Included CAs that are in or Ready for Discussion -- and A-Trust is listed there.
And what I think is the case here is that "A-Trust" has a root in the store from earlier on but their renewal efforts have not really worked yet. They're still stuck in that process.
Also: While expiration dates may not be a technical reason for exclusion from a trust store, expiration certainly is a reason according to Mozilla policy.