I'm pretty sure there are only two possible reasons for this:
I'm guessing (since you haven't posted the commands you used) it's this first one:
resize2fs (or similar for other filesystems) only resizes the filesystem, not the logical volume. You have to use
lvresize for that.
It used to be that you had to carefully specify a size to
resize2fs and the same (or greater) size to
lvresize (and mistakes lead to data loss) but nowadays LVM takes care of that for you:
lvreduce -r -L -1G rootvg/«opt2»
-r is critical, it instructs
lvreduce to first resize the filesystem (which generally needs to be unmounted and should be backed up just in case).
-L specifies the new size, and when given a leading
- it specifies how much smaller. «opt2» is a placeholder for that LV's name. Please check your system's
lvreduce man page to confirm your
lvreduce indeed has that
The other possibility is that you're using a very large physical extent size. The default is 4MiB (except with the long obsolete lvm1 format), so unless you upped the default by nearly three orders of magnitude, it's not that. You can check by running
vgs -o vg_name,vg_extent_size. Thankfully, you can change the size using
vgchange -s. Decreasing it is easy; increasing it can be a pain.