What you are showing is largely conjectural and based on the area surrounding the area of influence of all the city states (i.e. Mahajanapadas shown).
Maha=Mega
Jana=People
Pada=Place or conglomeration
There was zero tax collection from the shaded areas unless these were completely weak, backward areas with no one ruling them (given that some of these were BIMARU states even then, quite likely that they were backward then like they are today i.e, Bihar/Mithila, Madhya Pradesh and Uttar Pradesh areas). Agriculturally and financially backward with low GDP per capita today as well as before Mughal dynasty.
To Bhakts, all this "historifying" - is an attempt to recoup "lost glory" and re-write history so that they could revive the prestige and glory of "lost" Hindutva.
But there was little glory to speak of in any case and how can one "re-gain" prestige for something "lost" which did not exist ? Other than storybooks and colorful anecdotes.