How can there not be enough disk space to migrate

I don't understand what is going on here. When I tried to migrate a LR Classic catalog to LR I got the message below saying I needed 30.6 gigs on my Macintosh HD. As you can see from the second screen shot I have over 140 gigs of free space on that drive.  Can someone explain this?  The files in this catalog total only 76 gigs.