In large part because (in proper farming) vetarinary medicine clears out parasites harmful to humans which use the farm animal as a host.Um, honest question here: what's wrong with eating horse?
We eat all sorts of other animals. Why do horses get a bye?
This is in large part why the Bovine & Ovine tapeworm are rare in modern humans nowadays.
In Horses this vetarinary screening & dosing for food is not done with the inevitable results if eaten.
Humans hosting a tapeworm for example are notoriously anti social and somewhat dumb... & you thought the downtown lowlife wannabe mobsters were bad? ants seen nothing yet.
As an aside tapeworm host humans are also rather thin and have a drastically lowered IQ (reminds me of an ex republican president of recent history).
Also as probably noticed, humans are not all able to cope with Horse. Vaccine incompatibility for example has resulted in allergic shock versus the horse used as the vaccine host with crippling or more usually fatal results. A considerable number of other people actually have a food allergy to horse.
Wanna know why Clint Eastwood in the cowboy movies was always long tall & ugly? So did he...
It turns out that he is one of those unfortunate Americans allergic to horses, Any horse on his menu would see him on the john for the next day getting longer taller and uglier till it all came through.
That is why food labelling is in fact a very good idea and mixing is not a good idea unless you are lowlife catering for lowlife.
For the record I happen to be allergic to meat & bonemeal (MBM) which means that I still have a price on my head issued by lowlife in the UK during attempts to hide the BSE crisis caused by introduction of MBM into the food chain & the inevitable CJD outbreaks in the food stock animals it caused.
I am only able to eat correctly labelled meat and even then it is only possible because the MBM tainted stock in "fattening fields" was accidentally wiped out during the Foot & mouth outbreak of 2001.(its usage in the food chain was actually banned in 1997 so the continued usage by the lowlife food chain suppliers was not only illegal but illuminated by that outbreak).
Also for the record, the bulk of bonemeal was equine in origin in the late 1970s when the BSE outbreak began.
Have a nice day: Ag