It's human to be a little jealous once in awhile of people who have more than you, but you can't let it affect your outlook on life.
Instead of seeing it as these horses being 'forgotten', think of them as ones who hit the jackpot in life.
There are so many animals without proper food, shelter, or even basic care, that to be indignant about owners who may or may not ride their horses seems a little silly.
These animals are well cared for and their owners have made sure they have the best accommodations and training money can buy. That's a pretty sweet deal for them, whether or not they're being ridden consistently by their owners.