But experts say the reasons that years of aid have not curbed migration run far deeper than that. In particular, they note that much of the money is handed over to American companies, which swallow a lot of it for salaries, expenses and profits, often before any services are delivered. From 2016 to 2020, 80 percent of the American-financed development projects in Central America were entrusted to American contractors, according to data provided by U.S.A.I.D. The upside is that these companies have big offices capable of meeting the strict oversight requirements involved in handling millions of taxpayer dollars. The downside, critics say, is that a lot of the money disappears into those bureaucracies instead of reaching the people they’re trying to help. Half a dozen development experts who have worked with or for the contractors said the companies could easily take about 50 percent of the aid money they receive and direct it toward overhead — including generous salaries for executives — and company profits. When asked about that figure, U.S.A.I.D. did not contest it.