Should be noted that it isn’t geckos in general that don’t grow it back, just that kind (crested gecko). Though a regrown tail in other species still will be substantially different than the original
Different in what way? Does it regrow as an underdeveloped shadow of its former self?
Pretty much yeah. Heres an example from leopard geckos:
The top is one with the original tail, and the lower is one with a regrown tail
(Neither of these are my pictures, I just googled some for an example)
In this case at least (I’m unsure if every species is like this), the regrow tail doesn’t really regrow the bones or original bumpy texture, it’s just a smooth fat blob in generally the shape of the tail, though often a bit thicker, shorter, and more blunt at the end.
Skinks are the same way, no? They don’t regrow their tails after dropping them.