In bash, & just starts the program in the background, so all of the commands are run in parallel. You’re probably thinking of &&, which runs the command on its left, checks its return code, and then decides whether run the command on the right.

Although, in this case there are no ‘commands on the right’ since all the commands are on separate lines. You’d need to backslash the commands together, something like

pip install "$1" && \
easy_install "$1" && \
...

Not a typo, just an old formulation that’s sometimes used. See https://english.stackexchange.com/questions/52596/proper-usage-origin-of-the-generic-phrase-action-phrase-does-not-a-noun-mak for some discussion.

Could you post a link to what you’re referencing? I think I’ve read it before but I can’t seem to find it via web searches anymore.