Because they don't have that many fans. Upton Park or the Bowling Alley or whatever the f*ck it was called was old and needed updating, but it wasn't too small for them. And I don't mean that in a bad way, we've had disscussions on here before, in all reality we probably don't need a 55,000 seater stadium either, not at the moment anyway. West ham are what they are, but they didn't need more than 40,000 seats tops.