From The Cultural Life of the American Colonies by Louis B. Wright:

Not all seventeenth-century readers confined their interests to solemn treatises, but one should always remember that the prevailing attitude toward literature was so distinctly purposeful that many of our ancestors made themselves believe that they could gain instruction even when reading romances … few readers admitted even to themselves that they read merely for idle diversion …

Even at the end of the century, when settled prosperity had relaxed the more rigid life of the earlier period for many Americans, the proportion of trivial books that one finds recorded in inventories and booksellers’ lists is small … jestbooks , ballads, and idle tales were not characteristic of any colonial libraries that we know about …

If numerous copies of the History of Dr. Faustus were imported by Boston booksellers in the 1680’s and nineties, the reason must be found in the abnormal concern over magic and witchcraft in those years, not in a sudden shift to light reading.  When colonials bought books, they wanted something substantial, something worthy and respectable, something to do them good.