Back then we'd have like 50+ players in every zone.   Many peeps were on dial up modem lines - look up Wikipedia if you have no idea what this is - but basically it was slow ass and unreliable internet. 
 
Add to this computers that were maybe 1/20 as powerful (guessing) as a today's $200 android phone, and splitting big dense zones into smaller ones starts to make sense. 
		
		
		
		
		
		
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