Whats with MVNO's and their Parent MNO's?

We noticed a trend for many MVNO Carriers:

Aside from using their Parent MNO's Network Map and/or hiding who their MNO is deep in fine print (Terms), many MVNO's do NOT name who their Parent MNO Network is.

The only exception to this standard are MVNO's of the Sprint Network.
Sprint seems to heavily encourage their MVNO's to openly name them as the parent MNO Network.

But what about AT&T, T-Mobile, and Verizon?

It's like the only thing you see on those MVNO's is the same advertising slogans used by their parent MNO, but no real direct refernece to the MNO.

We should make it an industry standard, maybe even make a law to:
Make MVNO's openly list their parent MNO Networks on at least their coverage page.
Disallow MNO's from barring MVNO's from listing them as the parent MNO.

Some carriers in the past may have had a strange relationship about their name being used by anyone who wasn't an Authorized Partner - including their MVNO's. We get it, even though they are using your network, they are still competing for your customers. However, if they cannot openly admit who's network they are using, how can we trust that they actually have the coverage we have come to love and expect?

Obviously since they are an MVNO, you can still de-prioritize them on your netowrk when needed. So why is it such a big secret that they are using your network as if it was their own? They are paying you to do exactly that.