It's not 1987 any more and Excel doesn't use the file format that it used back then. The price of main memory and long-term storage has declined by many orders of magnitude since 1987.
Well, yes, obviously, but do you realise what a headache it is (would be) if the default behaviour of Excel changes? How many people would complain if things that used to work suddenly stop working with a new version?
The problem was that this default behavior was unchangable. Like, let me get into settings and turn this shit off (like they are now doing), they could have done this decades ago.