Perhaps more a physics question, but there is also a philosophical question why physics validate all measurements as the same. Of course one could ask why should one particular measurement be the only 'real' one.
Of course this is all about special relativity. But a bit in line of Ockhams'razor one could also suggest that the measurement with the less variable parameters should be the most right one.
But if one measure the length of something with a ruler just laying it besides it, it should be a more accurate measurement of the length of something than of the measurement of a observer in motion relative to that length. But in physics both measurement are equal in validity according to SR. Only light is absolute.
So the question is, isn't a measurement with less variable parameters not more accurate than one that is depending on the observers'conditions?