They reverse in Bradford because both stations are physically situated at the end of a line.
The line at Castleford continues beyond it and eventually merges with the ECML, but that section's only used by freight traffic. Or as a diversion if the main Leeds-York line is closed for engineering works.
( The Mock TurtIe ™ --- Thinks you are a cunt, on, Sat 3 Dec 2011, 19:14, Reply)