I would definitely not attribute it to any purposeful attempt at by a company to make things worse for older systems... human beings developing software on new hardware is already enough to make performance issues happen.

In reality, if the lead developers of some software find the experience to be good enough on their machines, that's going to lead to it becoming worse on old hardware, no matter what the company (as people have said in this thread, it's even worse with chrome and firefox.)

It takes huge amounts of effort to ensure that the development work you're doing is performant on a range of hardware. If you neglect doing that, I'd definitely chalk it up to laziness and not malice.

(In other words, I agree that performance gets worse from version to version, but you don't need to attribute to malice that which can equally be attributed to laziness.)