stencilface
High upon a hillside
Players and patrons are pretty intolerant of unnecessary rough riding and there is little affection for those players who are 'effective' if they are also hard on the ponies. The ponies are too valuable and it makes people angry to witness horse abuse.
What do people do when they realise, across country that they have got it wrong or that they are on course for a fall? It seems very similar to me.
Polo is a 'status symbol' sport - with both wealthy patrons who either have a true passion for the game and Polo 'culture' or who may want to use the game as a social 'entree' and the sportsmen who play either for themselves if they are rich enough or for their patrons. The patrons fork out huge amounts of money to enable them to participate and the sportsmen depend on their success to go up the rankings and to get more money, more playing opportunities etc. The ponies are either the property of patrons or players. They represent quite considerable investment and as an integral part of the game must be cared for.
Patrons do NOT like the approbation that cruelty brings them - it's bad for their social rise - at least in this country, and the players do not like or need to be criticised or left out because their pony skills are questionable. Some players are ambitious and play hard to win but a broken, injured or angry/upset pony is no use for anyone involved. Injuries happen and as always people do not always choose the best course of action for the pony.
I am just not sure why you have picked on Polo OP.
Ok, so I'm going to pick on eventing here, as imho is the forums favourite discipline, but substitute in anything.
Eventing is a status symbol sport too, many who support it do not really have any idea about horses.
There are many eventers who are well known for being hard on horses, yet owners still send horses to them.
A good percentage of eventers going at a reasonable level (Int and above) who are 8 years and above will IME have had some kind of serious vet intervention at some point. They may only be able to compete and be kept sound on injections, they may have been denerved in the case of PSD etc despite that fact its not allowed. They are iced above and beyond what imho is reasonable, ie people icing a bruised foot prior to trot up to numb it. Is this acceptable?