Except that ISO-8601 doesn’t include anything as useful as a political time zone, just an offset from UTC. That’d be good if UTC offset was useful for anything, but instead it just adds to the confusion.
Just have a look at the list from Wikipedia [1] and notice how many repeats there are.
As an example AMT could be either UTC+4 or UTC-4.
And this doesn't even includes the various local acronyms that people use around the world.
[1] https://en.wikipedia.org/wiki/List_of_time_zone_abbreviation...
IANA time zone identifiers are fully-qualified and unambiguous like America/Los_Angeles or Asia/Kolkata.
If you don't use these, you will inevitably be somewhat wrong due to leap issues, political changes in time, or the like.