Why do people loose faith in god who do they fear?

Very good question. People lose faith in God because they expect materialistic things from God.
ਨਰ ਚਾਹਤ ਕਛੁ ਅਉਰ ਅਉਰੈ ਕੀ ਅਉਰੈ ਭਈ ॥ ਚਿਤਵਤ ਰਹਿਓ ਠਗਉਰ ਨਾਨਕ ਫਾਸੀ ਗਲਿ ਪਰੀ ॥੩੮॥ AGGS 1428
Nar Chahat Kach Aur Aurai Ki Aurai Bhai || Chitavat Rehio Thagour Nanak Fasi Gal Pari ||38||
One wishes for something, but something different happens. Nanak says one plots to deceive others, but places the noose around own neck instead. To fulfil our worldly desires we make business deal or try to bribe God (Sukhna Sukhni) that if you fulfil my this desire I will donate this much amount to the Gurdwara or do Akhand Path or Langar etc. When the worldly desire is not fulfilled by the God then one start cursing God and start asking God what have I done to you that you are not fulfilling my wish? Why did you grant same to my neighbour? Why not me? Then one tries different corrupt means and lands in trouble resulting in spiritual (Moral) death.
2nd question is why people fear God. They fear God because they don’t know and understand God.
ਮਿਠ ਬੋਲੜਾ ਜੀ ਹਰਿ ਸਜਣੁ ਸੁਆਮੀ ਮੋਰਾ ॥ ਹਉ ਸੰਮਲਿ ਥਕੀ ਜੀ ਓਹੁ ਕਦੇ ਨ ਬੋਲੈ ਕਉਰਾ ॥ AGGS 784
Mith Bolara Ji Har Sajan Suami Mora || Hao Samal Thaki Ji Ohu Kade N Bolai Koura ||
ਕਉੜਾ ਬੋਲਿ ਨ ਜਾਨੈ ਪੂਰਨ ਭਗਵਾਨੈ ਅਉਗਣੁ ਕੋ ਨ ਚਿਤਾਰੇ ॥ ਪਤਿਤ ਪਾਵਨੁ ਹਰਿ ਬਿਰਦੁ ਸਦਾਏ ਇਕੁ ਤਿਲੁ ਨਹੀ ਭੰਨੈ ਘਾਲੇ ॥
Koura Bol N Janai Puran Bhagavanai Augan Ko N Chitare || Patit Pavan Har Birad Sadae Ek Til Nehi Bhannai Ghale ||
ਘਟ ਘਟ ਵਾਸੀ ਸਰਬ ਨਿਵਾਸੀ ਨੇਰੈ ਹੀ ਤੇ ਨੇਰਾ ॥ ਨਾਨਕ ਦਾਸੁ ਸਦਾ ਸਰਣਾਗਤਿ ਹਰਿ ਅੰਮ੍ਰਿਤ ਸਜਣੁ ਮੇਰਾ ॥
Ghat Ghat Vasi Sarab Nivasi Nerai Hi Te Nera || Nanak Das Sda Sarnagat Har Amrit Sajan Mera ||1||
God’ teachings are sweet and beneficial for all. God gives equally to everyone without looking at merits and demerits of anyone. God is nearest of the near as God’s abode is in everyone. As God is a philosophy, the teachings in that philosophy is, equal for all. Whoever lives life according to those teachings realizes God within. Nanak seeks God’s friendship and sanctuary forever who is the giver of spiritual life to all.
As we have seen that God is the wisdom in the word (Bani) of Guru. That means God speaks through Word of wisdom. God’s word of wisdom is sweet to everyone – sinners and non sinners. The wisdom does not differentiate between them. Even if sinners act on the wisdom they can be purified. That is how it is the God’s natural way to purify sinners. They will be in heaven now on the earth.
I hope it clarifies your doubts. You can read my book Gurmat Doctrines (Part1) available on amazon.com for answers to more such questions.