>>95793495
I’m assuming you meant to type “why did the ENTIRE town turn out?”
And yeah, it was to purge an outsider who learned too much. After the ambush to kill him in the hotel failed, he was loose and no one knew where he was. Innsmouth did NOT want information about the town getting out since… well, we all know what happens to Innsmouth once the truth about them go out.
Being an outsider might not be enough to get you purged, but being an outsider who knows the truth makes you public enemy No. 1.