I assumed that Hubble got more credit in America because he was an American, and because LeMaitre published in an obscure journal. But now I find that the NY Times credited LeMaitre all along:
In 1927, Georges Lemaître, a Roman Catholic priest and astronomer from Belgium, first proposed the theory that the universe was born in a giant primeval explosion. Four years later, on May 19, 1931, The New York Times mentioned his new idea under a Page 3 headline: “Le Maître Suggests One, Single, Great Atom, Embracing All Energy, Started the Universe.” And with that, the Big Bang theory entered the pages of The Times.The article goes on with some terminology history:
Over the years, The Times mentioned the theory often, and used a variety of terms to denote it — the explosive concept, the explosion hypothesis, the explosion theory, the evolutionary theory, the Lemaître theory, the Initial Explosion (dignified with capital letters). Occasionally, descriptions approached the poetic: On Dec. 11, 1932, an article about Lemaître’s visit to the United States referred to “that theoretical bursting start of the expanding universe 10,000,000,000 years ago.”
It was not until Dec. 31, 1956, that The Times used Hoyle’s term and then only derisively: “this ‘big bang’ concept,” the anonymous reporter called it in an article discussing discoveries that “further weakened the ‘big bang’ theory of the creation of the universe.” ...The theory has changed a little bit since LeMaitre, with the addition of inflation and dark energy.
By March 11, 1962, it was becoming clear that the phrase “big bang” had been co-opted by proponents of the theory. An article in The Times Magazine said that the sudden “explosion and expansion is by some called ‘Creation’; by others merely ‘the big bang.' ” ...
Today, when almost all astronomers have accepted the theory, The New York Times Manual of Style and Usage unequivocally requires Big Bang theory — uppercase, no quotation marks.