The pipe cannot change the value of the variable

wqfhenanxc@ubuntu:~$ Cat test.sh
#!/bin/bash
Lines=0
Cat $ | While Read line
Do
((lines++))
Done
echo "Number of lines read is: $Lines"
Exit 0
wqfhenanxc@ubuntu:~$./test.sh
Number of lines Read is:0

wqfhenanxc@ubuntu:~$ Cat test.sh
#!/bin/bash
Lines=0
While Read line
Do
((lines++))
Done <$0
echo "Number of lines read is: $Lines"
Exit 0
wqfhenanxc@ubuntu:~$./test.sh
Number of lines Read Is:8

The above two scripts one uses the pipeline to read the file, one using the redirect to read.
The result is not the same.
Ask for answers from the nature of script execution.

Background knowledge:
1. When I enter./test.sh on the command line, the current shell creates a child shell.
The child shell reads the commands in the test.sh and calls the fork before calling exec for each line of the command.

2. For pipelines, the child shell first creates the pipe descriptor and then fork out the two sub-processes on either side of the pipeline, allowing the output of one child process to be redirected to the input of another child process.