Why is it that the Jews are more sincere in their religion than the Muslims?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

In reality the Jews are sincere in their falsehood and forged religion, and committed great mischief in the land and became superior, but they will definitely perish. The main reason why the Jews are so is that the Muslims declined from leading the world because they became busy in this worldly life and were negligent about their obligations towards Allaah.

Nonetheless, this does not change anything; the Jews have gone astray whether or not they are sincere [in their religion]. It is confirmed that Ibn ‘Abbaas was asked: 'Why is it that the Jews do not become absent-minded in their prayer?” He replied: “What would a devil do with a corrupt heart? Allaah Says (what means): {…and the blessed end is for the pious.}[Quran 7:128].'   Therefore, the sincerity in performing acts of worship is praised and its doer is envied if these acts are righteous acts [i.e. if they are performed according to the Book of Allaah and the Sunnah of the Prophet ]. 

Allaah Knows best.