No Use / Of No Use?

swapanMy question is - why in sentence no. 1 'of' follows 'is' I mean put 'of' after 'is' and why 'of' doesn't follow 'is' in sentence no. 2 .

That's just the way English is.
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We say "It is of no use to" when we add the person(s) that it's useless to.

It is of no use to me. / It is of no use to you. / It is of no use to children. / It is of no use to the team.
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We say "It is no use" or "It's no use" when we add a clause with an -ing verb to show an action. We omit "of".

It's no use trying to help them. / It's no use speaking English. / It's no use buying that.

CJ