Do Dutch people not appreciate foreigners trying to speak their language>?

They probably don't understand you.  I found the Dutch people to be very friendly and welcoming.  If you go there and show respect and DO NOT be the American douche abroad ranting about how UNlike shithole America their country is, you'll get along FINE.  And they all speak English too! 

It is probably because Dutch to non-Dutch speakers is very hard to get right and pronounce correctly, and very hard for them to understand. If you speak Dutch and they revert to English, it’s probably a way of making the conversation easier, but they will have appreciated your efforts though. 

most of the people do appreciate it when you're trying to speak Dutch, i do. 

They are proud of their English, so they make it hard for people to learn Dutch. Not our best quality

Having lived in the Netherlands for a while as a foreigner, who taught himself to speak a bit of Dutch while I was there, I did experience that many natives were quick to switch to English when speaking with me, even if I spoke correctly in Dutch (from my accent it was always obvious I was not a native speaker). 

My opinion is that (for most, at least) they appreciated (and perhaps found some humor) in my attempts at their language. I think they switched to English not because of posessiveness or any negativity, but rather an assumption (usually correct) that their English was better than my Dutch. I appreciated their attempts to be accommodating and helpful, but I will admit, that it made it a bit frustrating to try to learn the language, as many people were quick to switch away from Dutch to English, even when I tried to speak it. 

Having said that, I loved my time there, and found the Netherlands, and the Dutch people to be wonderful! 

It could be that it's simply faster to use English, as their English is better than your Dutch. 

The most likely reason is that they are very confident about their own English. Even if your native language isn't English, many will demand that you speak Dutch or English. You see , there's this myth going around according to which English be the easiest language on earth (in reality Esperanto is), and another myth says Dutch is the hardest.

As the saying goes: dutch are proud of their languages, but not of their own

Probably you being rude or obnoxious.

I never had trouble when I attempted Dutch most were pleased to correct my errors.  Usually using the German word. My German was much better than my Dutch.

It might have helped the flag I wore on my pack.

I usually started out by asking something like

"Kan ik het eerst in het Nederlands proberen? Ik leer maar een klein beetje.

As it is a small language most are pleased you have been bothered to try and learn it.

Being polite for centuries it has been Dutch business policy to speak the language of the customer and not expect them to speak Dutch Started in the 1600,s

90% of Dutch report they can carry on a conversation in English.

77% speak THREE languages at conversational level.

The Netherlands has been named the third best country in the world for its citizens’ proficiency in the English language, according to the English Proficiency Index (EPI).

https://en.wikipedia.org/wiki/EF_English_Proficien...

I have watched waiters pretend not to understand obnoxious tourists.I was sitting with Dutch friend and he pointed out and said watch. After tourist left the waiter came to my friend who whispered something to him.

  The waiter then explained to me in FLUENT English what had happened.

I responded more or less with

De postkoetsier poetst de postkoets met postkoetspoets en postkoetspoetsdoek.

Not perfect but the waiter bought me a drink for the attempt. My friend was laughing too hard to order one.

When the drink arrived i said as thank you.

Als vliegen vliegen vliegen vliegen vliegensvlug.

I must have done a good job the waiter left the floor trying really hard not to laugh while friend howled  I finished the drink.before he could get control.

Many had been watching this incident.  Most being bilingual I also got some applause for my Dutch.

For the rest of night they would not talk to me unless I tried first in Dutch.

I can't remember the tongue twister they taught be that night. probably I was too drunk to remember but the beer was needed to loosen the lips.

I even learned Dialect and the naughty words not taught in school. I was  advised I should not use them until I was much better in Dutch.and gave me a few not as crude to use instead.

Why were you treated badly? Maybe because it was YOU!

French can be snobs. As my French teacher was from Paris I had a Parisian accent

And they would switch to English if necessary.

Why were you treated badly? Not being Honest when you tried a Foreign language.

You are wrong there, Dutch people do appreciate you trying to speak their language and they will speak Dutch back to you. I know this from personal experience traveling to Holland several times a year. The Dutch are among the most friendly people you will ever find. 

Snobbishness it sounds like. It must be a situation to where you have to be Dutch to speak their language or they will ignore you for trying to speak theirs. I know some French people who do this as well as if the language is only reserved for the French and no one else.