why mass,length and time are regarded as physical quantities?
Answers
Mass Length and Time are the quantities we feel we have a direct handle on. All the others are somewhat soft touchy feely empathetic sensations at the human level and statistical in their physics (as measurements).
Temperature is average molecular motions of stuff wizzing about. Luminous intensity depended on the quality of your candle making skills. Electric needed the rubbing of balloons on your jumper (or kites flown into thunderstorms), etc.
Obviously all those units have now been hammered into shape and have modern solid atomic scale measurement, but you won’t find an accurate instrument in your kitchen draw/cupboard (weigh scales, ruler, egg timer..)
Because they can be measured. For example a length can be measure such as 2much or 3m etc