The numerous logistical requirements of cycling afford more opportunities for loneliness outside of the activity itself- you can be lonely long after you've finished your ride by sinking many hours into waxing chains, investigating the cause of the weird rattle your bike is making, and figuring out routes on which you are less likely to be killed. The cumulative effect of this is ensuring no regular people will ever want to hang out with you.
On the other hand, cycling is more traditionally a group activity, so you run the risk of getting sucked into more unsavoury social pursuits. You might think you're a self-respecting lonely guy, but a seemingly innocent nod at a fellow cyclist can turn into group rides and coffee stops before you know it.