Why do Shias ask Ali for help and not Allah?

Shia Muslims pray to Allah in all their obligatory prayers. So this question is untruthful to begin with.

In addition, they ALSO seek the blessings and intercession and prayers of Imam Ali and other Shia Imams in the intercessory prayers. This practice is a continuation of what the Qur’an commands believers to do in relation to Prophet Muhammad. In Qur’an 4:64 and numerous other places, the Qur’an says it is necessary for believers to have Prophet Muhammad pray for them in order for them to find God’s forgiveness:

. . . If only, when they had wronged themselves, they had come to thee [Muhammad], and pleaded for forgiveness from God, and had the Messenger pleaded for forgiveness on their behalf, they would indeed have found God to be clement and merciful (4:64).

The Prophet Muhammad was an intercessor (wasilah) between God and humanity in the Qur’anic vision and the Shia believe Imam Ali and his succeeding descendants occupy the exact same intercessory role.

One may legitimately ask why intercession and mediation is necessary – why not just direct all prayers to God Himself and skip the middle man. The answer to this is that praying to God does not actually change anything in God; God is eternal and remains the same whether humans call His name or not. Neither 1 prayer nor 1000 prayers changes anything on God’s part. Prayer by a human being only changes the human being and this change allows the human being to receive more of God’s ever-flowing continuously bestowed blessings. Now this is where intercession comes in – the intercessor, whether a Prophet, Imam or Saint (wali), prays FOR the believer and the intercessor’s prayers help cause and bring out the inner change or transformation in the seeking believer. In other words, the intercessors prayer compounds with the believer’s prayer to have a greater effect on opening up and purifying the soul of that believer. Once again – this still causes no change in God because God is eternal and transcends time and space. But the believer’s heart changes – it becomes more receptive through his prayers and the intercessor’s prayers. Clear proof of this is the wording in Qur’an 4:64 and Qur’an 9:103.

In 4:64, the Prophet praying for the believers causes them to “find God forgiving and merciful.” This is key – God does not change from not forgiving/merciful to forgiving. The real change is in the believers whom the Prophet prays for – they are now able to “find” (wajadu) God’s forgiveness. It is the same in 9:103 where it is explicitly stated that the Prophet Muhammad prays for, cleanses, and purifies people by accepting their repentance offering and this he does on God’s behalf. But the Prophet’s role as intermediary and purifier is essential – this is why the 9:103 says that Muhammad’s prayers bring inner peace to the believers – reassuring their hearts with confidence that God accepts their repentance.