A simpler duplication shows the issue is below.

It appears the issue is  is not related to the "for loop" - it can be
duplicated just writing code inside the eshell { .. } block.

To duplicate, please create a file ccc.el.gz - something the gzip does not
fail on.

Then, On the eshell prompt, enter the following code:

 $  export aaa="This is contents of aaa"
 {
# create a variable in this block
export bbb=$aaa;
echo "Before gzip: aaa=$aaa"
echo "Before gzip: bbb=$bbb";
gzip --decompress ccc.el.gz;
echo "After gzip: aaa=$aaa"
echo "After gzip: bbb=$bbb";
}
Before gzip: aaa=This is contents of aaa
Before gzip: bbb=This is contents of aaa
After gzip: aaa=This is contents of aaa
After gzip: bbb=nil
 $

Same bug: After the call to non-elisp program, /usr/bin/gzip, a previously
exported variable bbb (exported inside the block) is nullified.

Thanks