I mean, in a way, you are changing the end of the work day (the work day will end a hour earlier in the previous time zone at one shift, and one hour later in the previous time zone at the other shift), it's just that the time zone shift is the mechanism we use to do it.

If we use the approach of having the workday end at 5 PM during one half of the year, and 6 PM in the other half, people have to ask themselves "Are we in the 5 PM half, or the 6 PM half?" This confusion will probably last for a few weeks, similar to the confusion when a year changes (I write the old year for at least a month).

On the hand, changing the clocks is a one time change, and then you don't need to constantly check which half you're in.