In the U.K. this is not true, as rule 61 of the Highway Code says.

Referring to cycle lanes and cycle tracks “While such facilities are provided for reasons of safety, cyclists may exercise their judgement and are not obliged to use them.”

The Highway Code defines what cycle lanes and cycle tracks are, they are different.

A cycle lane is marked on the road, with either a solid line or a broken line. Vehicles cannot drive in cycle lanes marked by solid lines or park in them. From my observations this is not observed. A cycle lane which is only half a meter wide are worse than useless. There’s not enough space between the bike and the vehicles, and does not comply with Highway Code rule 72. I recently saw useless cycle lanes of this nature in Guildford and Wallingford. This is the part of the road which collects debris.

Cycle tracks are routes physically separated from vehicles, so, they should be good. Unfortunately in the UK they are often poorly designed, with dangerous entry and exit points, obstructions, debris, poor surfaces and no right of way when crossing side roads.

Why would a cyclist not use cycle lanes and cycle tracks? For the reasons described above, the UK cycle infrastructure is often useless. The UK needs to look abroad to see how to make proper cycle infrastructure.