I'll say it again... LAZY. All horses are essentially lazy animals, that doesn't mean they are slow pokes, it means they want to get out of work and will express this fact in different ways.
Horse's aren't lazy. Never met one, never owned one, and I've been involved in thousands of horses over the years, of various ages, breeds, etc...
They can 'appear' lazy when they don't understand what's being ask of them. When they're sore, lame and in pain. When they're being asked to do something they can't physically do. When the relationship between them and their human is lacking. When they're turned into automatons with mind-numbing repetition. When there's inconsistency in training/riding. When they're being managed poorly.
But it's only an appearance. It's not real. But it's a fine excuse for the people to use.
I assure you, not one of my horses wants to get out of work. They thrive on it, the stimulation of mind, body and soul. To have a purpose, a motivation, and a rewarding partnership where the utmost respect and trust is demonstrated.