There is no such thing as height discrimination. Attractive qualities are always preferred. Otherwise soon there will be dck size discrimination. Lol
Just because it's not as severe as other forms of discrimination, doesn't mean it doesn't exist. It's also very much present outside of dating, for instance, in the workplace, where taller people are more likely to be promoted, and there's a positive correlation between income and height.
Heightism just really falls under the umbrella of "Lookism", if you want to call it that. It's just a sub-branch.
Look at the employees of stores - specially clothing stores. They tend to be taller than average if men, and better looking/slimmer than average if women. Societies are superficial and managers know that. They also hire based on looks. It makes sense for them anywhere where people will see their employees. Height is just one of the factors in the looks of a man.
Regarding the positive correlation between income and height, that's just Americans, the Swedes, and the Dutch being obsessed with making these studies. I'm sure this would also hold true for attractive people (i.e. attractive people make more money on average, establishing a correlation). However, websites would be more reluctant to publish any such findings with the ease they publish those "findings" about height.
Android even posted, one day, a study showing that taller people made more money, on average, when employed by others, but there was no difference in income among the self-employed; no such correlation with height, in the latter case. It's just obvious that the best looking people will make more money in any workplace where their looks are an advantage, and that they will also have an easier time being hired.