I'm confused - that's almost exactly what I said, albeit in a very condensed form.

Once you take a Discretionary bonus and then make it into an incentive (i.e. This year the Christmas bonus must be earned by doing X, Y, Z) and adding stipulations to the bonus that are tied to worker output turns it into a non-discretionary bonus.

Promissory Estoppel is the basis for why non-discretionary bonuses are a category. There is a perceived promise of a bonus that people work for, but then are denied which can cause knock-on effects for the people to whom that bonus is owed. A bonus is discretionary up until the point it's used to get people to work longer or perform better.

Sure the general term is Promissory Estoppel, but that's a much weaker regulatory framework than Pay and Labor laws around non-discretionary bonuses.

If there is something else I'm not understanding here please enlighten me further. If it's not "accurate" I invite you to help me be more accurate.