I just noticed that and was about to ask this too.
It is probably intentional as some other endpoints had their returned data reduced but it would be nice to have that information back.
Right now we can still get individual character data but we must fetch the character profile endpoints (and comply to the new game data policy).
As discussed here and later released here the profile specialization endpoint is far more complete and includes all necessary information. However this is kinda of an overkill for apps that only need guild related information.
Assuming a full guild at the cap of 999 players, you’ll need 1000 requests just to fetch character spec statistics for that guild. At the rate limit of 100 req/s you would take at least 10s for loading a complete guild info.
If we end up having to check /status for the new API data policy it goes to 1999 requests and at least 20s.
One use case for this is to break guild roster on a chart by race/class/spec/role.