Aside from depopulation agenda, they don't have the money to pay to old people (retirement insurance or whatever it is called in your country). Last week it was announced pension funds lost 3 TRILLION dollars (of course we know who they lost it to).
So there is no money left and another reason to get rid of old people (specifically) as soon as possible.
Also, with older gen gone, there is not that many left that remembers the good old days and our history, etc so they can feed new generation even more false info.
I am sure there are other reasons too that I can not think of ...
It is all WINS for THEM.