To some extent, people born in a religion can take it for granted and it can be uncomfortable to see people new to it who have so much excitement to do everything.
Here you are, you've been X religion all your life and you've settled into a groove with it, doing the parts that make sense to you and leaving some of it. Your name is X and your looks are X, so it has always been part of your identity and you don't have to do anything to hold onto it.
Now here comes someone who has just discovered how amazing and wonderful X religion is and he is doing every ritual and looks at you in surprise when you don't do something that is usually a part of X religion. This person studies and questions and asks about things you've never heard of before and their enthusiasm is exhausting and pretty annoying.
But converts can't help it!
Through Memoirs of a Jewminicana I found an article about a Jewish woman whose husband converted to marry her, but then took everything very seriously.
In the comments a girl named Rebecca said, "But realistically, who converts to be lukewarm about something."
You nailed it Rebecca. Someone told me about a year after my conversion that he was surprised at how familiar I was with services and rituals and how knowledgeable I was about Judaism in general. I couldn’t figure out why he would think I would be anything less. It’s hard for me to imagine someone converting who wasn’t passionate about it and didn’t want to immerse herself into the faith, the tradition and the community in a significant way.