Question about SSJ4 and Golden Oozaru

[Hulk10]

Wasn't it said in some official capacity that a Saiyan's tail actually stops growing back after Super Saiyan, because their body has evolved to no longer need it? On a biological level I'm sure those mysterious "S-Cells" have something to do with it too, where maybe having a high count of them inhibits tail regrowth.

Any way you slice it, rather than being "easy" it would actually be pretty rare for a Saiyan to meet the physical conditions for Super Saiyan 4.

Here's the exact quote, from a 2003 interview:

The tail lets you gain tremendous strength instantly by transforming into a giant ape, but the risks are equally great–you’ll lose your strength if it’s squeezed. Once you’re as powerful as Vegeta and Goku, the tail just gets in the way. It is thought that the bodies of Saiyans, who are a fighting species, decided that their tails are unnecessary appendages.

The weird thing is that Toriyama specifically cites the whole "tail weakness" thing as a reason for why they stopped growing back, despite the fact that both Goku and Vegeta overcame that vulnerability through training.

Yeah he probably did forget.