Well it doesn't HAVE to change. When GE pulled out of Horizons, they closed it a year later, because without a sponser "they couldn't afford repairs". But when UOE and WOM both closed for renovations, Horizons reopened due to a fluke. If it was closed, WOL would have been the only pavillion available in Future World East. Then they decided they put their Space pavillion there after years of planning to have one, because they could get a sponser for that. Then Living Seas went to a rehab without a sponser, but it stayed in it's original state for 7 years after United Technologie pulled out (minus the Sea cabs which only lasted three years). And WOL stayed opened for three years after Met Life pulled out because Mission: SPACE wasn't opened yet. The rest of the pavillions where rehabed WITH sponsers.
I'm truly no EPCOT expert but, I think Horizons wasnt build correctly. I think the foundation was not on stable ground and the building was shifting and they were afraid. I'm sure people in here have better knowledge on this subject than me. This is my recollection though. :shrug: