One common reason is that they arrived in London after their ship to
New York had sailed. Delays in travel can result in stays like you
describe until funds can be arranged because a new ticket must be purchased.
There is no credit for the ticket on the forfeited passage.

Joe Hirschfield
Portage, MI
HIRSCHFELD, HERSZFELD, LINDENBAUM, BUXBAUM, BUCHSBAUM-Skwarzawa, Zloczow,
Sielec Bienkow, Yaryczow Novvy, Glinyany-GALICIA
MINOFF, MINOWICKI, MINOWITZKI-Brest Litovsk, Wysoka-Litovsk

mrl@psfc.mit.edu writes:
Hi - I recently found a 1904 passenger list for a ship that sailed from
London to New York. Quite a few of the immigrants, were listed as having
been in London for a period of weeks (6-7) or a few months.
snip....