I wouldn't call it rudeness, it's more a habit, you might find it rude, but that is your interpretation. Holland is a really small country that survives by trading with other countries. The countries around it are all much bigger and tend to want to speak their own language (German, French, English) so it has become common that the Dutch person adapts instead of forcing the other person to speak Dutch.
Though funnily enough I will (during the summer) quite often get addressed in German when I enter a shop, at which point I haven't even said anything yet nor do I speak German.
Happens to me always at the Dutch Coast. Somehow I look a bit German.
I'm sorry if you consider it rude, but have you considered the people you're speaking to may have something better to do than to spend their time teaching you Dutch, or alternatively, may just believe you actually want to discuss the subject at hand rather than practice your Dutch?
If you want people to take the time and trouble to speak Dutch, consider asking them, preferably in a context without time constraints.
Well, I've never looked at it that way. Next time I will be more thoughtfull.
yep, the broken-dutch vs clear-english appears to be my experience too - if I'm in the right mood, I'll tease dutch people by speaking full speed english around them when they don't want to speak dutch ;)
People often explain it as kindness, but it's really just plain rude laziness: for many Dutch people, speaking slow and clear Dutch requires a lot more energy than upspeed English. Let alone listening to and trying to understand broken Dutch.