Almost always, but not everywhere. For US, yes, other American nationals make ~50% of their illegal immigrants, and that's a phenomenon on its own.

But take a bigger sample. Swiss were biggest offenders in Hongkong, Macau, and dozen other tropical vacation destinations.

Few years ago, Singapore's biggest offenders after Malaysians happened to be US citizens.

India, complicated story... but if you not count Bangladesh citizens, and stateless, I think almost all of OECD members will get to the chart

Vietnam, heard that they struggle with US citizens in recent years as well, though mostly Vietnamese Americans

African countries, a known story - tourist overstayers