TSS works by raising the 30 second smoothed power to the power of 4 and then reducing by the root of 4 after taking the average.
This is because generally the rate of production of lactate above your anaerobic threshold is a function to the power of 4 against the power output, and thus the training stress and normalized power is designed to account for the physiological cost of surges. And thus, sprinting skews the normalized power and thus TSS up because of the exponent and working at higher power.
This means that higher power skews the TSS up because of the exponent. I.e if you raise 2 to the power of 4 the answer is 16, whereas if you raise 3 to the power of 4 the answer is 81. Or an example in cycling, if your threshold is 300 watts and you do 600 watts, while you are producing double the power, the physiological cost is actually 16 times greater, as you are producing 16 times more lactate, not twice as much.
This though can be quite individual to the person, and some people are a lot more anaerobic and can really punch out high power numbers a lot more, which you may be.
To answer your question, it doesn’t fall down because TSS is just a metric to try and track the training load you are putting on your body based on the physiological cost of your efforts and ride, it isn’t going to be perfect but it will give you a rough idea of what you are doing and were you are at. And while TSS does equate various intensities and durations quite well, remember that not all TSS is created equal, think 2 hours at half of your threshold power will give you the same TSS as an hour at your threshold, but that is going to feel way different.
A lot of this comes back to the volume vs intensity debate, and requires a bit of subjective judgement on your or your coaches behalf and how you feel after various sessions and how it is impacting your plan and how it is leading toward you achieving your goals.