Trinity was a large map, with 30k(literally!) mountains or very long distances across oceans seperating the three countries and, originally, a big tank town area sheltered by 30k mountains as well. The tank town functionalyty was basically lost by global terrain changes after 2006, making TT an empty place.
With enough numbers and a working TT it was quite a popular map in it's day (pre 2006).
Without TT and especially with lower numbers it was very difficult to get action going across those 30k mountains, in particular during non US primetime. As this resulted in beign about the only map almost never being reset (which I was able to show a few years), we spent large parts of a tour on a map with such obstructions.
My guess is that this eventually led to its retirement. Shortly after its spot in the rotation was filled by CraterMA