I believe Google uses open data feeds from the transport operators where available, or online timetable data otherwise. Plus algorithms that learn from the real experience of tracking millions of smartphone users.
Clearly you have not used the app. I use it regularly and find it surprisingly accurate. Not perfect, but neither are NRE and the other rail planners.
If you choose not to try it, the loss is yours.
You are missing the point - you know it exists, and have experience that it is reliable.
I didn’t even know it existed and would be wary of using something not advertised as official.
Whereas everyone knows National Rail is official.
It needs a well advertised “National Bus” app that Joe Bloggs wondering how to get home can have confidence in. Or DfT to mandate and advertise a branded open data feed that Google etc can use to show authenticity.
Remember we are trying to get bus sceptics to give it a go.