They care about it a lot more than you imply, they just don't know that it's something they care about.

I partly manage a team of end-user support people, and the number of tickets they get with "my computer is slow!" is astonishing.

The number of times it's found that they have Slack eating over half the RAM of their corporate-issued laptop (read: wimpy specs) is huge.

The number of people who understand that Slack being an insane resource hog is a large part of what is making their daily computing business painful is the inverse.

Have you never had a non-technical person ask you to help because their PC is slow? Non-technical people care, they just don't know how much better it could be for them. They understand that their PCs are slow, and they understand how to close apps they aren't using to stop the computer slowing down. This habit even transferred over to phones where developers had to teach people that it's not necessary to habitually swipe background apps closed any more, because they were so used to doing it.

Users absolutely care if their app runs slower. Even marginally slower in the order of 1/10 of a second. Even subconsciously users will choose the app that runs faster and smoother, this is why google.com first page is optimized and compressed saving individual bytes sometimes. This is why all big websites use servers all over the world to save 10ms in ping for users which are near them.

The only debatable question is whether the exact memory overhead (of electron for example) on the specific user machines existing out there today will make a noticeable loading time or lag difference. For many users it seems it does, not everyone has the lastest hardware.

This is a completely arrogant view of users.

People quite obviously care about speed and latency issues, but they might not be able to pinpoint slack or discord, etc as the root cause.

People care about latency and sluggish interfaces on their brand new PC.