[jerf]

"One second every couple of decades" grossly, grossly overestimates our timing inaccuracies. Multiple orders of magnitude.

The problem is in some sense, the opposite... our timing is now so good that we can notice the natural variations in Earth's rotation to astonishing accuracy. Thus, if we want to keep the clock in sync with what the Earth is actually doing, we need to add the leap second.

(There's quite a bit of debate about that "if", and IMHO right now industry after industry seems to be experiencing major, expensive disruptions and repeatedly incurring risk, to save astronomers from having to consult a lookup table that they of course would build into computer programs and pretty much forget about ever after. But I digress.)

The Earth's rotation really does wobble by some amount due to natural shifts in density, temperature changes, and any number of other things. It's why we don't have a schedule of leap seconds for the future. If it were merely a matter of accurate timing we'd have a schedule, because our timing is accurate enough by orders of magnitude to make a schedule for a hypothetical perfectly-steady or perfectly-slowing Earth for millennia in advance. The problem is that we can't predict what the Earth is going to do.

[NickNameNick]

Astronomers use sidereal time instead of solar time anyway, so they're used to making time corrections, the sidereal day is only 23 hrs, 56m, 4 seconds and change. Equivalent to the length of a day if the light from the sun was coming from an infinitely distant source. That way at a given sidereal time, anything far enough away will always be in the same place in the sky.