Yes, the fighter has an incentive to hold off and try to spoil the wizard's spell... but the fighter also knows that (a) this guy is puny, and (b) he's got no armor. If you kill him NOW, he's not going to cast any spells anyway. And since you don't know until his number comes up whether he's going to cast, stab you, throw poison in your eyes, or something else entirely, you have to consider your options carefully.
OK, let’s all maintain our good sense of humor and take his one step further.
But if the fighter wins initiative and considers his options carefully, given the way the initiative rules are written and “ceteris paribus” (keeping all else constant) the optimal path is to strike the Wizard on the Wizard’s initiative number because that option delivers everything available via an earlier strike and could also spoil a spell. An earlier strike, on the Fighter’s higher initiative number, because it did not occur on the Wizard’s initiative number, could not spoil the spell unless it got a kill. In other words, the earlier strike must kill to spoil a spell whereas the later strike need only take place: hit, miss, or kill. So the later strike yields more net benefit.
A Wizard’s failure to cast does NOT deter this strategy. The fighter could simply key his strike to the Wizard’s initiative number. If the Wizard drops to 1, then the Fighter can strike then to avoid wasting the round – and still spoil any spell – because that’s the last possible initiative number on which the Wizard could cast and any cast concurrent with a strike fails.
Both paths result in the Wizard suffering an attack, but the delay by the Fighter ensures that he will foil (or suppress) any spell. This you-can-drop-your-number situation in conjunction with auto-spell-spoil creates a heat seeking missile situation where the attacker is compelled to key on the spell caster - ceteris paribus.
And, we have to keep all else constant. Why, because if you say, “If the Fighter waits then the Wizard’s Dwarf buddy could attack and kill the Fighter before he strikes.” Then I could counter, “What if the Fighter’s Elf buddy kills the Dwarf before he can strike the Fighter.”
I feel like that guy in Princess Bride.