Not a musician but married to a composer and pianist.
Old scores are not precise in the way that modern ones are. A lot depends on little things that were never written down, particularly if the composer performed the work himself; ornaments (trills and the like) would be put in at the performer's discretion, and in the 18th century at any rate, performers were expected to supply a good deal of ornamentation themselves. There is a definite trend over the years of specifying more and more exactly how the composer wants the music to be played.
Another aspect with something like the Goldbergs is that many players will now play it on the piano, for which Bach wrote nothing. The mechanics of the harpsichord or clavichord are very different, so that the modern score editor has the option, if not the obligation, to insert dynamics or pedalling that are only appropriate to the modern instrument.