Why do horses get put to sleep with broken ankels ???

My opin.. they should never of been in that sorry condition..i hate horse racing with a pion... i hate what they do to racking horses also. Poor things have no choice on the matter.. taken advantage of by their owners. I just cried when eight belles went down. Saw it on the news.. Her breaks were too severe to heal. If they kill horses i think they should kill humans too when they cant get well also.. But this is just my opin..