Why do Americans celebrate St Paddy's Day in the US, when hardly any Americans have Irish blood?

If I'm not mistaken, Americans are fully English and they are direct descendants of those Pilgrims. And they remain English to this day, no?

Miller, Johnson, Smith, Robinson, Walker and Hall don't sound much like Irish names, do they?

I think St George's Day 🏴󠁧󠁢󠁥󠁮󠁧󠁿 would be a more suitable holiday for them, but that's just me.

Anyway, I live in the UK, so what do I know?

Why do Americans celebrate St Paddy's Day in the US, when hardly any Americans have Irish blood?
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