It must feel funny to be a German speaker learning Dutch. To me it would feel strange to learn a language very closely related to my own. Danish and Swedish are mutually intelligible (at least some dialects are), so someone from Copenhagen and someone from Gothenburg can hold a conversation in which one person speaks Danish and the other person speaks Swedish each with their usual accent. I’ve witnessed that.
If the other language is mutually intelligible or almost mutually intelligible, then taking that step further and learning the language would feel like putting on an accent that you don’t normally have. It would be like putting on an American accent to speak to Americans or a Scottish accent to speak with the Scots. I think I would find that embarrassing and kinda like being phoney or fake.
I don’t know if that’s true, but that’s what occurred to me on my walk this morning.