Why do the non- shiites deny the Waliat of Imam Ali, when its clearly mentioned in the Holy Quran?

my quran contains 114 surahs and im shia. however, i can find many a proof for this very concept just within those surah which are in the universal quran. the only problem is....i dont know when Allah (swt) will choose to guide you....and hence i dont know when any of you will be willing to listen.