>The tensor product itself captures all ways that basic things can 'interact' with each other!
In quantum physics, "interacting" usually has a different meaning. So one should use these terms more carefully.
>And you need the tensor product already for pure states in QM.
No. Pure states are just vectors (or more precise: rays) in Hilbert space. The usual inner product is sufficient to work with them. An outer (=tensor) product of these states will just give you a density matrix with tr(ρ^2)=1.
Keyword is can. There's a reason why most university level physics curricula defer quantum density matrices (and by extension tensor algebra) to more advanced classes. There's a lot of mathematical legwork required before you can actually make use of that.
"The tensor product itself captures all ways that basic things can 'interact' with each other!"
Tensor Product is also the way to go when combining classical probabilistic systems.
And you need the tensor product already for pure states in QM.
(mixed states need density matrices)