Just because a phenomenon can't be industrialized doesn't mean it doesn't exist; you can't industrialize lyric poetry, for example.
So until the 1880s, there was no commercial exploitation of these compounds, yet they nevertheless existed either in actuality or potential. Once there was an understanding of the principles and the development of some related chemical and biochemical processing, this exploded and had a dramatic impact on human life.
If someone postulated in, say, 1785, the idea that perhaps there were specific compounds that could be used to cure infection, and these could be produced en masse, would it not be analogous to respond that since nobody is commercially exploiting (at the time), they clearly do not exist?
None of the ideas included in the xkcd comic are particularly new or obscure. Despite being pigeonholed as a certain kind of bullshit, they are still ideas that a lot of people have heard about and been hearing about for a very long time—more than enough time for someone to get around to commercially exploiting if that were in fact practical. Ghostbusters came out 37 years ago, and the stuff it made fun of was familiar enough to its audience.
However, in 1785 the principles of chemical engineering were largely unknown, precluding the development of a modern-style pharmaceutical industry. It did not, however, prevent widespread use of antibiotic treatments that we now understand the mechanism for and can refine or synthesize into more effective forms.
(2) It is intriguing to consider commercial music as an industrial utilization of lyric poetry, but the point is that the individual activity of lyric poetry is not amenable to industrialization IN ITSELF, but it still exists. But perhaps this example doesn't work -- the really important argument is above, namely, that the cultivation of these practices -- astrology, dousing, etc, is individuated, and oriented around virtues directly opposed to their mass utilization.
(3) As other commentators have noticed, we also don't know that these sciences aren't used on a mass technological/industrial fashion --- it seems likely, for instance, that there are corporate entities that use i ching divination, and likely, too, that there are financial firms that utilize astrological methods -- but wouldn't reveal this because of the likely opprobrium from a still dominant (if clearly declining) orthodox materialism...