Why won't Indian IT companies allow a person to play the same role till retirement? Other sectors allow this. Even in US, I have seen people working as developer or tester or DBA at the age of 60.

I don't think there's a hard policy against that, but at some point the economics of it doesn't make sense. Imagine yourself as a fresher at Wipro, you'll earn 3.x LPA as a junior dev. Now if you don't want to get promoted, the company still would have to give you an appraisal to keep up with their norms of equal treatment and basic inflation deterrent. let's say you managed to stay 10 years in Wipro as a junior dev. With a 10% increment every-year, you'll end up with ~9 LPA salary for a junior dev. This goes against Wipro's pay band for junior developers which hasn't changed much in the past 10 years. In developed economies, the inflation isn't that much, so the annual appraisal is also very less. Doesn't affect the band even if you work at the same job for a decade.

Because y’all feel that 50L for 2 yoe is less than market value. If you want to get paid market value, you have to increase what you bring to the table :)