why the late updates?

hello
i've had my s6 edge for just over a month now having had previous galaxys before
here in the UK its been about 2 months since Marshmallow rolled out for Samsungs
since joining these forums i've noted Samsung are lets say dragging their feet over updates
forgive my ignorance but aren't most phones in similar categories running the same stock Andriod and if so why wildly spaced roll outs?
i'm just wondering why say Nexus will get N update up to 3 months before Samsung? and LG are really...

why the late updates?

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