Personally, I highly doubt Disney has the testicular fortitude to do that these days. Along with that, the current resort was expanded during Eisner's time as CEO to accommodate the typical US family's 7-day vacation. Further expansion on any kind at a theme park level throws everything out of balance and would cannibalize the existing parks, water parks, Springs, etc.
That's a fair point to an extent. However, times have obviously changed in several ways:
First, there are simply more people in the parks on a regular basis than there were in the Eisner era. The lines are simply longer throughout the year, even during off season.
To be fair, recent stories HAVE come out showing that the early May off season is easing up again. Nonetheless, time will tell whether that's signs of a total "back to what it was pre pandemic" or not.
Which leads me to the second thing: Increasing use of annual passes. From experience, if you have the whole year at your hands to go to the part, there's more of a desire for variety.
Third, park hopping. Now obviously that's been a thing with resort guests, not just pass holders. But still, pretty commonplace.
Fourth, since anyone can walk into Disney Springs without tickets or passes, it's not necessarily a key part of the 7 day vacation you mentioned. Anyone in Orlando or Kissimmee can head over there for shopping or dinner or what have you. For the vacationers, it's more of an extra.
Let's put all that together, while looking at the 7 day vacation of the resort guests. You have 4 parks and two water parks, with park hopping as an option. That's six. Disney Springs as an additional thing if you have extra time, but that's not exactly top priority. So a 5th gate takes care of the seventh day. And if "We couldn't do everything," well, there's the whole "leave the audience wanting more."