That was in a Presidential election year after Obama had already appointed two other Justices and the vacancy was the deciding vote, and Garland was more of a centrist than the previous nominees but was still left-leaning and would have flipped the court. Then they definitely lose if they confirm him but maybe win if there is a President from the other party the next year, and on top of that as long as they held the Senate even if they didn't retake the Presidency they could just confirm Garland in the fall instead of the summer.

That's not what it looks like in most cases. In the first half of any term the next election can't gain you the Presidency but it could lose you the Senate. On top of that, when it isn't the deciding vote, e.g. the first of either Alito or Thomas to be replaced, a moderate is a much better hedge than the coin flip even in the second half of a term, because if you take the moderate and then lose the next election at least you have the moderate in the other party's majority, meanwhile if you win the next election then you keep the majority regardless.

Which is to say, that's only likely to happen in the next few years if it happens for the second of the two Justices in the second half of a Presidential term and the Democrats lose the subsequent Presidential election.

The way you make that tougher to accomplish is by adding more checks and balances or repealing laws granting excessive authority to the executive. Packing the court would de facto remove an important one. The thing that would help that is a constitutional amendment prohibiting court packing.