I know most of this thread has been about making fun of Slack, but I wanted to write a somewhat serious response to this.
I think "team software engineering" plays a big part of this, if not even the main reason. When one developer is working on a program, the person tends to be able to keep track of program flow, memory usage in their head and know when things are about to go out of bound, memory shoots up, etc. When you have a whole team working on a huge piece of software, each person is working on one part of it at a time. If your feature grows memory usage by 100mb, it's not a big deal. 20 people doing that, memory usage just grew by 2gb. And then in modern software dev shops, you typically put devs on different features on a weekly basis. (unlike traditional, slow, non-agile development where a person owns a certain module/component and is the expert and works on it for years) When you move to a new feature, you need to pick up on all the details of how it works previously, and you build your stuff on top of it. You don't have context of the really nitty gritty details someone who wrote the original framework thought about. You're going to do something less than ideally efficient. Unfortunately, this is just the way modern team software engineering goes.
Or of course, you can still just say it's a Javascript problem and mock JS; which also has merits.