Do Buddhist monks beg for food?

Yes, for they believe they should spend more time in practicing Buddhism and devoting themselves to it than wasting time in earning money, but they don't realise that the people they beg from are capable of giving them because they earn money. So if not earning money is going to help them to achieve Nirvana (which they believe is ultimate peace) then why should someone else earn for them and not achieve Nirvana?