People generally worship these Gods so that they can get their blessings and rewards for their worship. This worship to Gods is for the fulfillment of their desires, rise in status and position, for health, wealth, for their wants, freedom from sufferings, for getting off-springs, for marriage and other desires.
However, this type of worship done by those people is not proper and their fruits are limited and temporary because it is done for the material rewards. Lord Krishna in Shrimad Bhagwat Gita says as follows:-
"antavat tu phalam tesam
tad bhavaty alpa-medhasam
devan deva-yajo yanti
mad-bhakta yanti mam api" (Bhagwat Gita: Chapter Seven verse 23)
"Sri Krishna said: Men of small intelligence worship the demigods, and their fruits are limited and temporary. Those who worship the demigods go to the planets of the demigods, but My devotees ultimately reach My supreme planet."
But as per Lord Krishna in Shrimad Bhagwat Gita one should not ask for all these material desires from the Gods but should be devoted to Supreme God (Lord Krishna) only as then God shall not only give everything but shall also protect, whatever, a person is already having. Not only that, in the end Lord Krishna shall give salvation (Nirvana, Mukti, Moksha) to that person.
The essence is that, whatever you want, material or spiritual, you can get it from God by becoming His devotee. God Himself declares in "Bhagwat Gita"
"ananyas cintayanto mam
ye janah paryupasate
yoga-ksemam vahamy aham" (Bhagwat Gita: Chapter Nine verse 22)
"Sri Krishna said to Arjuna: But those who always worship Me with exclusive devotion, meditating on My transcendental form—to them I carry what they lack, and I preserve what they have."
Jai Sri Krishna.