There's a secondary dimension to this:

You can still micro-optimise for memory and cpu performance. That's certainly a thing that is possible to do.

Alternatively, you can buy more cpus and memory.

What has changed in the past few years is that for many workloads, the cost of buying more cpus and memory is significantly lower than the cost of all the development work to optimise away the need. Hardware is cheap compared to developers, for many applications.

There are still some applications where this is not the case, and in those cases people still care about memory management.