According to the die-hard Novus Ordinarian:
They are just fad followers.
According to the indult:
Traditional Catholics follow the Old Rites by courtesy in order to combat the wickedness so rampant in this world more effectively and worship more effectively while keeping up with the current framework and reverently and pass some good customs to the next generation. Those TLM-onlyists are just nuisances to the Church because they are uncharitable and hinder the progress if the Church.
According to (the average CI user? the SSPX?):
Traditional Catholics stay with the Old Rites because it's the only working Rite in order to combat the wickedness of this world, helped by the decline of the Church. VII actually didn't help the Church gaining more relevancy nor extending Her hand to distant areas, it actually weakened the Church against the dark forces by making evangelism harder, denying the access to certain Sacraments, invalidating the exorcisms, stripping the Mass of its' value, etc. We need to pass our good customs and values, ever present in the Tradition, to the next generation, which they obviously don't get in secular schools, clown liturgies which made the Church ridiculous, and the media which even corrupts them. There is a possibility that the systematic weakening of the Church was deliberate and was faciliated by the enemies of the Church. The indult is making compromises. Our Church is collapsing and we are trying to slow it down and possibly, stop it.