Why are the trend for electronegativity and ionization energy similar?
Well look at the definitions for each property......
Pauling drew upon (i) ionization energies, and (ii) electron affinities, measurable atomic properties to construct his scale, i.e.
For each property, the magnitude reflects the nuclear charge. Atoms with high ionization energies, i.e. atoms of elements that appear to the right of the Periodic Table as we face it, should also possess high electron affinities, and form negative ions facilely. This is indeed the case for oxygen and fluorine.