Comet tailing is the long persistence of very bright highlights due to insufficient beam current to discharge the photosensor in one TV field.
Here's an example:
https://www.youtube.com/watch?v=l4qamJ1cDfo
Edit: common places to see this were on brass band instruments and women's jewelry or sequined dresses.
Saticons, Plumbicons, and similar tubes have the problem. Special design changes were made over the years to reduce it: diode electron guns, which produce cathode rays with a lower variance of electron velocity (a lower "temperature"); plus special circuits that sense the highlight and momentarily increase the beam current (but reduce the resolution momentarily also).
And yes, SD camera tubes lasted longer.
I think the reasons for not making larger tubes were several, all having to do with increased cost: entirely new and bigger lenses (TV cameras already needed special lenses with long back focus to pass the image through the long path in the prism block); new larger prism blocks; possibly, difficulty in making larger faceplates/targets with good uniformity (requiring new manufacturing equipment as well). Also, a larger faceplate would have more capacitance, making it harder to get the high frequency response needed.
I will note that due to the smaller image size than 35mm film, the depth of field was increased compared to film. It was hard to sell HD as a movie making technology, because cinematographers felt they had plenty of depth with 35mm by using a smaller lens opening, and wanted the capability to
reduce depth of field and blur the background more in many shots.