This is unfortunately a major annoyance when it comes to Mileage Plus on TG flights, it's been that way for several years if not longer. I see these all the time intra-Asia involving TG where it's a zero mileage fare, but with TG, the price difference between the discount fare and the next fare class up is usually pretty significant, basically pushing me to another carrier because at that point TG doesn't make sense anymore. (For example, RDM/PQM eligible fares on CA, BR, or SQ are usually lower than TG's lowest mileage eligible fare if crediting to UA Mileage Plus.)

TG sometimes offers some really great intra-Asia fares but they're absolutely worthless if needing/looking for PQMs. Their PQM earning fares (Economy class) generally aren't competitive.

I've seen UA Mileage Plus adjusting the earnings charts again recently, some good, some bad. It wouldn't hurt to shoot an email to the Mileage Plus Service Center as a gentle complaint about that fare class. Never hurts to bring it to their attention again and maybe it'll get changed (for the greater good, even if you never fly TG again). I have noticed some previously ineligible fare classes are eligible for at least partial credit now on other airlines.