The gates started in Miami. As PRO of the Tornado course, we were asked to experiment with various courses to make Olympic sailing more interesting, easier to follow, more spectator friendly, etc. This was an edict by the Olympic folks with the added note that if sailing didn't start making money it would be eliminated.
So, we got to work and tried a bunch of stuff during the Miami Olympic Regatta.
We tried gates at the weather mark (really wild and exciting but very dangerous)
gate at midway down/up wind (eliminating banging corners and allowed spectators to see who had the lead other than at the top and the bottom. Also, allowed spectator boats closer to the starting line without interfering.)
Gate at the bottom (still used)

We determined that 10 boat lengths was very good and personally I still think that is what it should be. Get much closer and you risk having overlapping double two-length zones.., lots of confusion and probably lots of Protests.
I was part of the RC at the Olympics in Savannah and in charge of the gates.., sort of. Paul Ulibarri was PRO and kept insisting the gates be set as close as 4 to 6 boat lengths.
And I do not think the sailors were very happy with that setting. After all these boats are really hauling and two boat lengths goes pretty fast. 10 BLs apart allow for a bit more time for decisions.
Rick