The reason is because it's a nuisance job - a builder won't do all of the elements you want.
He may do the break through and lintel and move the stack, but a builder won't fit the window, won't move the socket, nor make good the plaster / render. So a builder would have to get in subbies.
It would be a pain to coordinate the trades and it would be hard to make any money.
Are there any extensions being built in your street or nearby? - you could pop your head in and ask. A builder might be interested if it's 100 yards or somfrom another job.