Right. The problem is that there are two fundamental reasons for dealing with time across the globe, and their solutions are generally mutually exclusive.
Reason 1 is synchronization. Knowing if an event happens in place X at time T when that happens in place Y. This is what universal time simplifies.
But universal time messes up the other reason for dealing with time across the globe, which is knowing what part of the day it is in other places.
While timezone conversion pretty readily allows synchronization across the globe, universal time doesn't have a readily-available solution for knowing what's going on in New Zealand right now. (It's 2:30 AM there, so probably not a whole lot, but you knew that as soon as I said 2:30 AM, which is the whole point.) You are still going to need to have some way to say what the current time means in other places. This is automatic right now. Two in the morning means the same thing everywhere. A universal time doesn't. So you'd have to say something like, "It's currently time T, which in New Zealand is several hours before sunrise." So you're basically coming up with ad-hoc local times anyway.
Reason 1 is synchronization. Knowing if an event happens in place X at time T when that happens in place Y. This is what universal time simplifies.
But universal time messes up the other reason for dealing with time across the globe, which is knowing what part of the day it is in other places.
While timezone conversion pretty readily allows synchronization across the globe, universal time doesn't have a readily-available solution for knowing what's going on in New Zealand right now. (It's 2:30 AM there, so probably not a whole lot, but you knew that as soon as I said 2:30 AM, which is the whole point.) You are still going to need to have some way to say what the current time means in other places. This is automatic right now. Two in the morning means the same thing everywhere. A universal time doesn't. So you'd have to say something like, "It's currently time T, which in New Zealand is several hours before sunrise." So you're basically coming up with ad-hoc local times anyway.