I don't get it but most people, IMHO, do not like being called out for their accent. That makes no sense to me.... to me a heavy accent should be one of your most prideful characteristics.
I think they believe you're 'making fun of them'... which I suppose happens... but if I notice you have an accent and mention it it's out of pure respect and admiration.
One of those Agriculture magazines called me once about a subscription. The lady on the phone was from Mississippi. now not ALL people from the south have a pronounced accent but this lady was a master. I got lucky... because I HAD to bring it up and it made her get giddy. Didn't bother her in the least, she was proud of it, actually... which made me all the more fond of her.