Why people get title sir?

The Sir title can theoretically be conferred by sovereigns (ergo: countries and/or kings and queens who use English language) by the way of conferring a knighthood.England, Queen Elizabeth II and their Sir titles that go along with knighthoods are very well-known.

However, in the Philippines the title Sir comes together with a knighthood of the Knights of Rizal, which is a fraternal semi-governmental organization with public law corporation status since 1951 when this was signed into law (Act 646 of the Republic). So, in the case of England the title emanates from the sovereign in the person of the Queen and in the Philippines it emanates from the sovereign in the form of the law of the Philippine Republic.

Sir titled knighthoods emanate also from former colonies of Britain that still accept Queen Elizabeth II as their head of state.