Analysing the number of representatives in various countries, that number is in no direct proportion to the countries' population. In Poland we have the 460 representatives in lower chamber and 100 in higher chamber, with the population of 40M.
The number of representatives is more the compromise between the possibility to represent various political movements and the effectiveness. With 40 representatives it would be hard to represent all big political movements with proper proportions, but imagine 10.000 representatives! The people should know their representatives, and with too much number of them it would be impossible to know even a procent of them. And the work of parliament would be paralised, if each of this 10.000 would like to take a speech.