Why don't all wind tunnels use magnets to suspend models?
Two reasons:


When a model is suspended in a magnetic field, and then the wind tunnel is switched on, you'll see a change in the force along 'y-axis' (The lift forces) and change in force along 'x-axis' (The drag forces). Hence, you'll need a complex mechanism for sensing this forces, and changing the magnetic field in such a way that the change in forces is compensated by the 'change in magnetic field' so that the model does not translate in any of these directions and stays static. Then you'd measure the change in magnetic field to measure the forces, and hence the system becomes expensive and cumbersome.
For pressure measurements, you'd have to use wireless sensors on the pitot ports, as you dont want tubes dangling form the suspended models. This makes the process more cumbersome and expensive


This is why the magnetic suspension is not used every where, as the cost to accuracy ratio in normal wind tunnels is much less than the ratio in magnetically suspended models of magnetic wind tunnels