Target hardening. Any anti-theft device can be defeated, but the harder and more burdensome it is to do, the smaller the pool of thieves willing to steal under a given set of circumstances is.
Bicycle locks are very easy to defeat, if someone has the knowledge and readily available tools to do it - but not everyone does or has it on them.
It's easy to just cut the grab handle or the steering wheel, that's how 'the club' is commonly defeated, - but not everyone has a cutting tool on them.
No steering wheel lock will prevent a drag-and-tow steal - but not every theft involves a tow.
So, you're more likely to deter the more amateur and low end thieves, but won't slow down a prepared pro in the slightest.
