Why not should except hike in TCS,even if we have 6 lak+ employees, anyway they are getting bill for all 6lak emp, then what are the reasons

Even though they are charging from clients for all 6 lakh employees, do remember that in year 2024 if they are earning 100₹ in profit (easy example) after removing all expenses... If they provide hike to all 6 lakh employees, the hike would be given out of that 100₹ profit only. So they give minimal hike.

If they have to give really good hike to everyone in TCS, their profit would reduce to 60₹ instead of 100₹ next year.
Why would they do that?

And also, you can't ask client to pay more just because employees need good hike every year. There is a certain set of rate charge for each level/designation of employee which continues for many years before some increase in rate charge happens.