I Don't really see the reason why some soldering tips come with a hollow core.?

 

Lower thermal mass? Lower cost?

 

If I understand your question....

A very popular style of soldering irons use a heating element that extends inside the body of the replaceable tips.

The tip slides over the white ceramic heating element and a ferrel slides over the tip and body of the soldering iron to secure the tip in place.

 

Most of the ones I have are only 0.12" dia. hole
The rest are solid core.

 

For vacuum desoldering? I use hollow tips for the task... On the other hand, I use hollow back tips for my Hakko soldering iron and there are many others that do. I would make a SWAG that it heats the tips quicker with that mode of design.

 

These are not hollow tip, just the body, I have ordered solid copper tip versions instead of the plated kind; see if they perform better.