The weight that an ingredient adds to quality has to do with the ilvl of the ingredients (ilvls taken from the Gamerescape website):
Roasted Coffee Beans: ilvl 110
Mineral Water: ilvl unknown, but likely around 4
Sweet Cream: ilvl 6 (HQable)
Maple Sugar: ilvl 1 (HQable)
Cinnamon: ilvl 4 (HQable)
Filtered Water: ilvl 70

The HQable ingredients in this list are all VERY low ilvl, and so add very little weight to the quality of the synth.

Now, take a look at Bacon Broth:
Smoked Bacon: ilvl 110
Xelphatol Spring Water: ilvl 110
La Noscean Leek: ilvl unknown, but likely 90 (HQable)
Garlean Garlic: ilvl 11 (HQable)
Volcanic Rock Salt: ilvl unknown, but likely 55 (HQable)
Black Pepper: ilvl 14 (HQable)

Garlic and Pepper are still low level and don't add much weight (though, both are still higher level than any of the HQable ingredients in the Coffee), but the heavy hitters are the Salt and Leek. The fact that they're high level add a lot of weight to quality - though the fact that the Water and Bacon are even higher level means that the weights of these ingredients still don't add a whole lot to the quality bar.

This is why there's a huge disparity between the Coffee and the Broth. The HQ ingredients in the Broth are much higher ilvl than the HQ ingredients in the Coffee.