How?

It shows it at the point of access request. If 2 programs request access 5 minutes apart, how would you show that in a single window?

Do you suspend the first program and wait until another application makes an access request? What happens if another doesn't make a request in a given time period? Will the user wonder why the first application has stopped doing anything useful for 5 minutes?

Honestly, how would you show this in a single window?

You certainly could, however I guarantee a huge majority of users wouldn't read a lick of what they were agreeing to.

Individual popups don't completely solve this, but it makes more obvious that a specific application is requesting a large amount of permissions. They're a bit more digestible to the crowd that won't bother to read an alert longer than one line.