Why does alot of the fan base not use these character's last names

[Bob74h]

Like

senju tsunage
uzumaki nagato
yuki haku
kaguya kimimaro

These are characters all with pretty well confirmed surnames yet nobody addresses the characters with them

 

[Charlie]

We didn't know their parents last name, right? Like, we know one of Tsunade's parents is Senju but she could get surname from other one. Same with Nagato.

 

[L o g i a]

Like

senju tsunage
uzumaki nagato
yuki haku
kaguya kimimaro

These are characters all with pretty well confirmed surnames yet nobody addresses the characters with them

Because they aren't necessary to identify the character - people do the same shit with OP characters
There's only one Tsunade*
only one Nagato
only one Haku
only one Kimimaro etc. etc.

In fact I think the only duplicated name in the story is Sasuke, right?
Do you address people in real life with their full names?

 

[Flower]

We didn't know their parents last name, right? Like, we know one of Tsunade's parents is Senju but she could get surname from other one. Same with Nagato.

This. And it‘s also possible none of Nagato‘s was called Uzumaki and he just had Uzumaki heritage. Same for Karin, actually.