Why does it cost more to repair my watch than what it's worth?

Many times it will cost more to fix an older watch (Bulova,
Gruen, Elgin for examples) than they cost new (back then).  It
may cost $250 to repair your Bulova but when you think of
how much a new watch (today) would cost for the same
quality (several hundred), it would be to your advantage to
repair the vintage piece.  It may be several hundred dollars to
repair your great grandfather's pocket watch, but, by looking
in a 'price guide' you find your watch only lists for $100 or so.  
Would you
not repair it because somebody said your watch isn't
worth it?  This watch might be all that you have from this
person, this might be what ties your lives together, I think it
sounds like it's worth more than a hundred bucks, don't you?