Star Trek: 10 Things You Didn't Know About T'Pol
6. The Ratings Dropped And So Did Her Neckline
As the show entered its third season, T'Pol's character underwent a number of changes. First, she left the Vulcan High Command. This led to her receiving a field commission of Commander in Starfleet by the fourth season. One would assume that she would then be issued with a Starfleet uniform, like the rest of her crewmates. One would assume.
Costume designer Robert Blackman was quite honest when describing the reason for T'Pol's costumes. He said it was simply to boost ratings. As the show's second season wore on, the views were beginning to dip, so the show began to plot out the Xindi Arc. Along the way, T'Pol's darker catsuit was abandoned for brightly coloured variants with plunging necklines.
Though obvious, the costumes continued to provide her with outfits like this for the rest of the show's run - even when she entered Starfleet. Rather than a Starfleet uniform, she was given another low-cut jumpsuit with rank insginia. While the ploy may have contributed to the show receiving a fourth season, it wasn't enough to save it from cancellation at the end of that year.