Source: every discussion I've ever had about how to deal with storing dates in databases, date comparisons, etc
If Timezones are difficult for programmers to model into our systems, then they are likely difficult for everyone to model in their brains
Simplifying the model benefits everyone, not just programmers
"what time is my colleague available" and "what time is that in my timezone"
With just the first one
The biggest advantage of getting rid of timezones is when an absolute point in time is mentioned, e.g. the start of an event. It's so annoying when the start date for some global event is announced and they only include a local time in some obscure timezone.
If you're going to live-stream an event for the whole planet to see, use UTC. It's especially baffling that organisations such as SpaceX or NASA use local time instead of UTC. You'd think that anyone dealing with things in orbit would use UTC.
If time zones where abolished you do t have to worry about what time zone a written time is in (is the 7 eastern or central or GMT or etc) its always 7 UTC.
Then you can take the SAME knowledge that East Coast of the US is 6 hours behind UTC, to figure out that 13:00 is the morning for them.