Merging various sed commands is not working well

I am trying to compress an html file with following steps using sed command:

Remove comments by sed -e :a -re 's/<!--.*?-->//g;/<!--/N;//ba'

Remove blank lines by: sed '/^\s*$/d'

Remove leading spaces by: sed 's/^\s*//g'

Remove trailing spaces by: sed 's/\s*$//g'

Merging all lines into one by: sed ':a; N; $!ba; s/\n//g'

Above commands have been taken from different sources on the web including Stackoverflow answers.

When I chain above commands using pipe (|) operator, it works very well. However, when I try to use a single sed command, some functions are not working:

sed -e :a -re 's/<!--.*?-->//g;/<!--/N;//ba; /^\s*$/d; s/^\s*//g; s/\s*$//g; :a; N; $!ba; s/\n//g' 

The comments are not removed and the blank spaces are also not removed, though all the lines are getting merged into one.

Where is the problem and how can it be solved?

> Where is the problem

The problem is that some commands are intended to work on each line of the file, while N appends the next line into pattern space and b modifies script execution flow. This causes further commands to be executed only on the end of the file, with no more lines available to read.

Note: to parse XML files use XML parser, not sed.

> how can it be solved?

It can be solved by "programming" - analyzing the purpose of the sed commands one by one and analyzing the intended flow of each sed script and rewriting the code that will work as intended.