Why did others drop out of early color manufacturing?

[David Roper]

I suspect the almost universal adoption of the pumpkin shape mask in 1949 was an answer to Zenith's porthole design. It's obvious from the visual aid above that the same tube appears much larger with the pumpkin mask (or none) than with a rectangular mask and, of course, size matters. Philco's 7" sets are the only ones I'm aware of that retained the 3:4 rectangular mask in 1949-50.