Because most work cannot be broken down into ideally independent tasks.

Considering how many of these companies have been able to operate perfectly, grow, launch products and post record profits over the last year and a half goes to show that that thinking is outdated and wrong.

This is just absurd, JIRA wouldn't exist if you couldn't break down work into independent tasks. You're effectively saying assembly lines can't exist. Tasks can be completed by individuals regardless of where they are.

I work with a company that has teams spread out across the country and we collaborate via video and text chat all the time. It's just as effective.

Here's the thing, if you are in a big company and you work with people all over the country, you can still collaborate with them via video and text chat. It would be the same experience whether you are in the office or at home. In those circumstances, those tasks can be done due to the means of collaboration still being equally effective.