If almost all commuters are car drivers, then there won't be many bikes buzzing around inconveniencing them. And if there are enough bikes to inconvenience the drivers, then there are enough to justify investing in their own infrastructure.

Actually the City of Cambridge installed a bike counter on one of the main thoroughfares toward one of the bridges over the Charles River into Boston. There are more than 1000 trips in each direction on a weekday.

Traffic congestion and inconvenience are caused by cars in vast disproportion to bikes. The sheer volume of car traffic is the primary predictor of congestion.