He wanted to win the no-bell prize!
or
Because they don't fit on a ironing board
or
Billllyuns and billllyuns. Light bulbs are part of the interstellar "goo" that pervades our universe; they are star stuff.
or
he got a little behind in his work.
or
They screw millions of bulbs every day, but when it comes to your bulbs, there's no record.
or