Because the legal release of Saints Row: The Third uses CEG (Custom Executable Generation) DRM. This means that my exe is different from your exe is different from user bob's exe. A trainer often works by poking at bits of memory and changing values which is made exponentially harder, if not outright impossible, when trying to deal with this type of DRM. It's also why you haven't seen anything similar to SR2 Powertools, which has other modding functionality in addition to the slowdown fix, for SRTT.