Because they are siblings of the same gender. It's difficult for people to remember which is which sometimes, regardless of names. So it adds another level of complication when the names are similar. And even worse if they are twins. And even worse if they are identical.
Three boys nappin', one mama namenerdin'
To peruse my top 100ish names:
http://www.behindthename.com/pnl/82589To peruse my non-name musings:
http://jodifriesen.blogspot.ca/