The issue is that while _some_ users only experience the surface level of packages like PyTorch, Numpy, SciPy, Pandas, and so on, people who actually have to develop these packages must work with the C++ and C underneath. To the developers, the problem of Python's performance is front and center, and a real issue they face every day.
So, the developer folks will make the switch first, as they realize it's much nicer to develop Julia packages in Julia than it is to develop Python packages in C. Over time, this will mean the development power switches to Julia - and as soon as these developers have build tools as good or better than existing tools, the majority of users will slowly migrate, too.