There are various reasons for poverty in developing countries. Some reasons include:
1. High-level government corruption
2. Weak rule of Law
3. Weak Government institiutions
4. Wars
etc.
However, one of the single biggest reasons could the Debt Trap
Due to low income, the government has to borrow money to develop infrastructure projects. However, due to corruption and various other factors, the country is never able to pay back the money it borrowed, leading it to fall deeper in debt.
In countries like Pakistan, the single biggest government expense is paying off the debt, which means that money for education, health, etc is largely reduced.