If we did the same thing with time zones or leap days, that some committee would only announce changes a few months in advance then people would get very upset.
And daylight saving is a local problem. In my country the rules have not changed for more than 4 decades.
The other problem is that most systems use time zones and daylight saving mostly as a presentation format. Only time that is explicitly for human consumption deals with time zones. Internally computers mostly use UTC.
The problem with leap seconds is that computers often represent time as some number of seconds since an epoch. That requires a stable conversion between year-month-day-hour-minute-second to seconds since epoch.
And that's where leap second are a problem. Because future leap seconds a undefined, this conversion is undefined for dates in the future.
That then results in a collection of hacks to let it work most of the time.
Where I live, civil time is currently off by about one hour and 41 minutes, compared to solar time. It is safe to say that essentially nobody cares about solar time with more precision than one hour. If you want to know about sunrise or sunset, you just look it up. Noon is mostly irrelevant.
The DST offset isn't known until that moment.
This does happen, with daylight savings.