Actually bitumen does flow. It's an extremely viscous liquid. There are a couple of pitch drop experiments[1] running, where bitumen is placed in a funnel and allowed to slowly flow. The experiment at the University of Queensland opened the funnel in 1930, 9 drops have flowed out since then, the last in 2014. The period between drops after air conditioning was installed seems to be in the 12-14 year range (only 2 drops have happened in that period).

[1] https://en.wikipedia.org/wiki/Pitch_drop_experiment

That's a viscoplastic. Banana, chocolate, and dog droppings are some common examples.

AFAIU, it's a liquid, and it does flow, it's just that it flows so slowly it's almost impossible to notice

https://en.wikipedia.org/wiki/Pitch_drop_experiment