why groovy each function not iterating while inside another one

why groovy .each function is only one time iterating while it lies inside another one iteration like shown below code ?

Code:

@Grab('com.xlson.groovycsv:groovycsv:1.1')
import static com.xlson.groovycsv.CsvParser.parseCsv
import groovy.xml.MarkupBuilder
import groovy.xml.StreamingMarkupBuilder
def input = "input.xml"
def xml = new XmlSlurper().parse(input)
df = new FileReader("file.csv")
def writer = new StringWriter()
def data = parseCsv(df, readFirstLine: true)
new MarkupBuilder(writer).root {
    xml.children().each {
        it.attributes()
        println ("Here I am")
        data.eachWithIndex { row,id->                     
            println ("This line should be iterated all time") // but iterated only one time             
        }
    }
}

Output Comes like this,

    Here I am
    This line should be iterated all time
    This line should be iterated all time
    This line should be iterated all time
    Here I am
    Here I am

Expected Output:

Here I am
This line should be iterated all time
This line should be iterated all time
This line should be iterated all time
Here I am
This line should be iterated all time
This line should be iterated all time
This line should be iterated all time
Here I am
This line should be iterated all time
This line should be iterated all time
This line should be iterated all time

That's because parseCsv returns an Iterator, not an Iterable:

See in source code of groovycsv library:

static Iterator parseCsv(Map args = [:], String csv) {
    new CsvParser().parse(args, csv)
}