Why are alkyl iodides generally more reactive than alkyl fluorides?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — halogen Modern version of the periodic table of the elements.

The reactivity of alkyl halides is primarily governed by the strength of the carbon-halogen bond. In general, there is a direct correlation between bond strength and reaction rates: the stronger the bond, the slower the rate of reaction.1

Alkyl iodides are more reactive than alkyl fluorides because they possess the weakest carbon-halogen bond among the alkyl halides, whereas alkyl fluorides possess the strongest. Because the carbon-fluorine bond is exceptionally strong, alkyl fluorides react so slowly that they rarely undergo nucleophilic substitution reactions. Conversely, the relatively weak carbon-iodine bond allows the halogen to be more easily lost as a negatively charged ion, facilitating faster reaction rates.23