Dockerfile make only runs using one thread

[C0rn3j]

RUN make this is in the Dockerfile for cuda build, why is not enabled to use all threads by default?

It's only using 1 out of 12 threads on my machine. It took ages even when I actually did set it to RUN make -j$(nproc), can't imagine how long it would run without.

Is there a reason for this limitation?