The top of 最 is 曰 (to speak) The bottom half is "to take, grab". From the dictionary, this character is listed in曰 radical. "To take your words back is the utmost difficulty" hence its meaning.

最的部首是“曰”yue1 以曰为部首的还有eg：曷；替；曼 此外，以日ri4为部首的有eg：旦；旧；早 etc.

A simple answer to your question is that 曰 (Say, verb) and 日 (Sun, noun) are two different hanzi. They look very alike but they are totally different. If you want to ask me Why? Because it is Chinese and the history reformed them many times. In American English, you may find "Check" (verb) and "Check" (noun) (from Cheque) are two words even they look the same.