If memory serves, I read on Absolute Ultraman that the reason it ran for so long was its popularity. TV Asahi originally ordered 50 to 52 eps, but when the show got really popular they ordered another 10 to 15 eps. Then the Suguira scandal came along and they made a compilation of the last 2 eps after which they aired 2 eps of Ultraman Neos in Cosmos's time slot. But after the trial got settled, they decided to start airing Cosmos until its finish. The scandal was the reason that all but 4 or five eps didn't air on TV.