Most plungers don't make a good seal.
Just about every plunger on the market today is round, but the drains in most toilets aren't centered in the bowl, so the plunger doesn't make a good seal on all sides.
The simple solution is for toilet manufacturers to include a plunger that fits the exact shape of each model and include it in the box when you buy it.
Because each plunger would be form fitted for the unique position of the drain, all your plunging troubles will literally go down the drain.