A big factor is that Java was the entire ecosystem, you're getting a programming language (which is pretty good), a novel virtual machine (most of their ideas fell through but the basic thing is fine), dedicated hardware (mostly now forgotten), a component architecture, and a set of tools for them.

You're still on this 1GB/core thing which is the wrong end of the scale in two senses. Firstly, I've worked on systems where we'd want 1TB/core and so today that means you're buying a lot of CPU performance you don't need to get enough RAM because as you say, that machine is "exhausted" anyway.

But more importantly the scale for big products isn't dictated by RAM or CPU it's dictated by service provision, and at large scale that's just linear. Twice as much provision, twice the cost. Avoiding a GC can let you slash that cost. Cutting a $1M annual bill in half would justify hiring a Rust programmer though likely not a whole team. Cutting a $1Bn annual bill in half - which is much more like what Microsoft are spending on O365 - is obviously worth hiring a team.

It's not instant. GC tuning is basically instant. RIIR might take three, five, even ten years. So don't expect results tomorrow afternoon.