Why don't British kings and queens veto laws?
I've learned from Wikipedia that the British king or queen has the right to veto laws, but they don't use the right. Why is that? Is it because of tradition, respect for democracy, some regulations or perhaps something else? I'm asking because the presidents of my country (who are however elected by the people) have an analogous right, and they use the right quite often.
The monarch of the United Kingdom is, as are most contemporary monarchies, a historical artefact, with little (if any) political power, their role is largely ceremonial. Refusal of royal assent is rarely exercised any more, and the main reason is, as you suspected, respect for democracy. Conversely, the last time royal assent was refused in the UK was in 1708, when Queen Anne vetoed the Scottish Militia Bill.
Elected officials, on the other hand, are not going against democratic structures if they exercise their veto powers.
kinda untrue, they DO use their right to veto : http://www.theguardian.com/uk/2013/jan/14/secret-papers-royals-veto-bills
@NinjaNoel That's not necessarily correct: according to a palace spokesman, "The sovereign has not refused to consent to any bill affecting crown interests unless advised to do so by ministers." - i.e. they maintain that the elected government was really behind withholding consent, and ascribing the veto to the Queen would be like claiming the Queen is actually ordering the military around (i.e. technically, but not really). Also, consent is different in details from conventional veto; veto happens _after_ a law is passed (overturning an actual act), while consent is needed to even discuss it.