I think a lot of it has to do with the common part of culture philosophy:

'Mine is bigger than yours!'

if your next door neighbor or best friend has a huge TV, one always has to one-up it with an even bigger set. it's been that way for years. even during the Muscle Car era it was sorta similar, but with speed. 'mine is faster than yours!'

It's not expected to stop. but i must be one of very few humans who has evolved to the point that it makes absolutely no logical sense. to me screen size means nothing if the set cannot live long enough to really enjoy it. i prefer this philosophy the most:

Quality, NOT quantity.