Why don't some Operators Track? Have First Glasgow ever Tracked? McGill's used to and are no longer on there.
It depends who has public live tracking feeds pretty much. There's lots of sources though such as bus open data, local transport authorities, operators direct, etc etc.
First Glasgow doesn't have an tracking feed that is open to the public (as far as I know).
The feed that was being used for McGills (and various other Scottish operators) the data wasn't very good and there was no way to link the tracking to an actual trip, so the data was quite poor really for passengers. I don't think the feed was really meant to be used for the purposes that bustimes was using it for, and certainly wasn't of the normal tracking schemas, so it was a bit useless.
On the plus side, with Scottish BODS seemingly starting soon, these operators will hopefully start sending data there, and bustimes I am sure will make use of that open data.