Solubility vs Dissociation of HF
I think your last sentence answers your own question very well:  


  It is because it forms strong hydrogen bonds in solution and thus forms
  stable solvation spheres (solubility), but its high electronegativity
  prevents $\ce{H+}$ atoms from leaving its vicinity (dissociation).


Dissociation is one mechanism of dissolution, but not the only one. Also, however, the $\ce{H-F}$ bond strength is not solely determined by electronegativity.