Expand Layer arrow not visible even when adding new shapes

[Jacobson Made]

I'm working with an illustrator file from a client and there are several layers that should have sublayers but there is no expand layer arrow to show the other objects. 

[Jacobson Made · Accepted solution]

SOLVED: In the Layers Panel menu, under panel options, make sure to untick Show Layers Only. Why would anyone want that option lol.

[Oshino Studio]

OH MY MAN!
I've been struggling with this for years ! 
receiving various files with no possibility to look inside ! got completely stuck so long until this day !
Indeed WHY? WHY would anyone do/need that? 
Thank you so much !