Because, generally speaking, it's Catholics (and Tractarian Anglicans) who celebrate the Vigil/Eve of a Holy Day (All Hallows being All Saints' Day, and Halloween being its Eve).
For some reason, and I'm not sure when, a lot of people mixed up All Hallows' (1st Nov) with All Souls' Day (2nd Nov)and decided that Halloween was about returning souls/hauntings.
I haven't heard a single firework, and don't expect to - hurrah! I don't like loud bangs, whichever day they happen!