The article contains one possible clue: gelatin melts at body temperature. This implies dishes made with gelatin melt in the mouth like chocolate does, but I can't recall experiencing that (at least not to the extent of chocolate) when eating gelatin-based stuff. (And many gels, at least in my opinion, have a better mouthfeel when more solid than liquid.)
Agar is great for a gel, especially one you want to stand up to a bit of heat and remain stable at room temp, and I would always reach for it instead of gelatine when doing most desserts or pastry work. OTOH I would only use it in a sauce if I needed to accommodate a vegan guest.
As an alternative, I've found methylcellulose to be pretty good for thickening my vegan homemade sauces (mainly tried it because I use it for other stuff, like fakemeat homemade protein sources). That's for homemade mayo or the like; for sauces in stews and similar, flour does the job - though US cooks seem obsessed by cornstarch instead for that use case.
Probably just tradition. It's pretty easy to "accidentally" make gelatin when making a broth, and intentionally making it only requires heat and bones, which are essentially pure waste. Whereas agar is a product that you have to buy in a store, and wasn't even available in the West until somewhat recently.
Of course, everybody just buys gelatin in the stores these days, and agar is almost as easy to find, but old recipes tend to be handed down for generations.
There is a family story that I had been fed a good deal of agar as a baby since my parents were poor but my father was at a state university and the agar was able to walk out the door with him from lab classes (and I think he worked as a lab assistant/technician to pay for school).
Also, they simply aren’t perfect replacements for each other. Agar and gelatin are certainly similar in many ways, but the are not the same.
The traditional jelly around the outside meat of British pork pie would frankly be weird texture (and probably horrible) if it was made from agar. It really has got to be made from pork bones to be authentic. It does melt in the mouth, when the pie is properly made - sadly rare these days.
Agar-Agar, the Parisian artsy synth-pop duo - "How do we find out if we already live in a simulation?"
With our warming climate, I wonder if research is happening to develop heat-resistant agar, similar to coffee, cocoa, and rice.
We were often a bit horrible given to practical jokes back then (1970s), but I also remember exploring an unused store room (fighting off giant cockroaches) and coming across a litre (or two?) of pure 100% Analar ethanol, which made for a merry lab-rat party (not drunk straight from the bottle) for all.