There are a few reasons. The first was that France's crises were resolved more quickly, and earlier (by the end of the 18th century) than those of some other European countries (more like 19th century). The French Revolution might have induced emigration to the U.S., except that it was tied up with threat of foreign invasion, meaning that many were caught up in the patriotic fervor of the time. Also France, unlike many other countries, enjoyed a long period of "peace and prosperity after the Napoleonic Wars (except in 1870-71, while other countries' upheavals were just starting. All this meant that French 19th century emigration to the U.S. was less than those of many other countries.
A second reason was that the French had other landing spots in North America. One of them was French-speaking Quebec (Canada). A second was French-speaking "Louisiana," which didn't become part of the U.S. until 1803. And as a commenter pointed out, the French (and British) also had landing spots in Africa and Asia (e.g. Algeria and Indochina). So the French emigration was not fully reflected in French immigration to the U.S.
A third issue was that French immigration to North America (Canada, the 13 colonies or Louisiana) started earlier (17th century) than that of most other countries (except England). Put another way, the wave of French immigration started earlier, meaning that the 19th century wave was smaller by comparison to the more visible 19th century waves of other countries. Basically the French did a large share of their emigration before the U.S. became the U.S; the people of other countries did theirs afterward.