Winning is not the only motivation though.

If I was playing against Steph Curry, I would try to come up with achievable goals, such as trying to defend well enough to force him to take a jumpshot instead of a layup, trying to make one of my own shots, trying to get him to fall for a pump-fake, trying to get a steal, trying not to fall over, etc.

Winning may not be, but there's always an achievable goal you can strive for.

Doesn't seem like you are playing to pass the time, in that case. Seems like you are playing to win. The difference is in the former case the play is the reward in itself and in the latter case you need to feel victory over someone. Seems crypto-competitive and kind of weird for that reason.