Because it has nothing to do with entanglement, which is a necessity for non-classical computation.

Instead the use case is isolating a two dimensional 'slice' of electrons on the surface of a 3d substrate.

Simply put your question is like asking why can't you use a lathe to make a bolt of cloth: they are fundamentally incompatibile technologies.

Cool study, although this website is abhorrent. The gist of the experiment is proof that a unique state of matter, known as a quantum-spin Hall state is stable at room temperature in a Bismuth Bromide compound.

This has applications not for what we think about as quantum computing, but instead its sister technology Spintronics, or 'electron spin transport electronics.'

The benefit of this tech is while it only does classical computations (the same as our current silicon gate technologies), it is immune to the 'leaky' quantum tunnelling effects that limit the size of our transistors.

Theoretically with spintronics you can produce absurdly tiny processors, even down to the molecular scale. This would be useful for ultra-low power / size applications, such as sensor clouds and nano-robotics.