Horner's not getting a contract because he's going to get destroyed next year.
At 41 and end of his career, Horner had nothing to lose by pushing whatever cheating/doping strategy he had to maximum effect. If he got caught, no big deal - he retires. While younger riders may have been afraid to aggressively cheat or try something new, Horner had no constraints.
Now that Horner proved that whatever regimen he was a guinea pig for works, everybody else is going to start using it. Every GC contender is calling up his doctor and saying, "I want what Horner had."
Playing field will be leveled and Horner will get the results one would normally expect a 42 year old cyclist to get. His *** handed to him.
Also next year: superhuman record times and a very small number of cyclists will f-up the Horner regimen, push it too far, and get busted.