It's cheaper to make unoptimized software. Business is not interested in making it fast, as long as users don't complain. And that's how we end up with software that's just fast enough to keep users from seeking alternatives.
Yes, take MS Teams for example. Takes around 1000MB or RAM. Older chat apps used way less. IRC used less than 1MB, sure it didn't do voice or video, but it could do things Teams still cannot do.
Here's some amusing threads 18-19 years ago when people were complaining that it was using over 20MB:
https://www.neowin.net/forum/topic/273565-msn-messenger-7-at...
https://www.neowin.net/forum/topic/442458-msn-messenger-75-e...