Present them benefits of learning new and improving existing skills (which can be done via other ways that just with books). Getting raises for being more efficient, opening career alterations that are closer to what someone desires (like a web developer moving to become a system architect), keeping themselves viable in the current market so that either they can move to new positions (generally you get better increases in pay switching jobs than just earning raises) or to provide career safety should something happen to their job (even the best workers can get laid off through no fault of their own).
If they still think that watching TV, going to their kid's ball game, or rock climbing is where they want to spent their extra time, then that is fully their choice.
Now, if their skills are becoming outdated enough that their performance is dropping or they are at risk of being laid off/replaced, that is between them and their manager, and your input should only be given if they request a suggestion from you.
If their lack of expansion is hurting the team as a whole, you should carefully approach the team lead/manager about this, but make sure to package the message carefully. ("Hey boss, I think if we got some training in XYZ we could be more productive," is good. "Hey boss, employee A not knowing XYZ is hurting our team," is bad.)
In short, the answer is incentives. You can explain the incentives (or if a manager, perhaps even offer incentives). But if the incentives aren't good enough... well that is their choice.