It’s a long standing tradition for the losing candidate to quickly concede to avoid delegitimizing the President elect. Does Trump have a right to contest the election until it’s certified? Yes. But as usual he has no respect for traditions and the wisdom they hold, and he is selfish and completely lacks grace.
And before you bring up Al Gore, that was a completely different scenario. Literally 300-500 ballots in Florida could’ve switched the results of the entire election that’s how close it was, Trump on the other hand has absolutely NO viable path to victory. To think he could overturn Georgia, Pennsylvania, Arizona, Nevada with a combination of recounts and lawsuits? Utterly ridiculous.