You seem to have 2x 3TB drives in a RAID1 configuration (mirrored). So you can only use 1x 3TB worth of space, but if one drive dies, the data is still available on the other one.
You can't expand the /home partition because there is no unused space to expand to. The drive is fully in use, about 1TB for / root partition and 2TB for /home partition (plus a small /boot partition).
So there is nothing wrong with the install per se, it's fully utilizing the available hard drive space.
To make the /home partition larger, you'd have to shrink the / root partition accordingly. However, that is not easily done in a RAID setup without LVM.
Unless you wish to reinstall, break redundancy or do in-place conversions, the easiest solution here would be to just make use of the space by putting some of your files on the / root filesystem, too.