I think when people get Borrelia using these "unorthodox" ways, it's probably also because of some low immune system status that allows that to happen (and a bit of bad luck).
Let's remember that when the tick bites the host it injects its saliva which has immunosupressive effects, and that allows the infection to get the foothold it needs :
"We conclude that tick saliva affects the chemotactic properties of chemokines and AMPs on immune cells and has an antialarmin effect on human primary keratinocytes. Alarmins are mediators that mobilize and activate antigen-presenting cells. Inhibition of cutaneous innate immunity and of the migration of immune cells to the site of the tick bite ensures a favorable environment for Borrelia. The bacterium can then multiply locally and, subsequently, disseminate to the target organs, including joints, heart, and the central nervous system."
www.ncbi.nlm.nih.gov/pmc/articles/PMC3028856/