https://www.ftcap.de/en/products/ele...rs/axial-lead/) doesn't show the tube amp versions, I assume that they are custom order types for big amp OEMs and amp parts distributors. Probably size and shape were chosen/specified to make them suitable as drop-in (authentic looking) replacements in vintage type (Marshall etc.) amps.
There is some temperature benefit from large cans and chassis mounting.
F&T makes smaller sized axial types with higher temperature/lifetime ratings as well.