Why do religious people want other people to say grace?

Ken Gallinger's ethics column in this Saturday's Star (which, weirdly, hasn't been posted online) has a letter from someone whose friend has recently become religious and now wants to say grace before every meal. But rather than saying grace herself, she says to the assembled group "Who's going to say the blessing?", trying to bully someone else into doing it.

I've heard of this happening quite a number of times in different contexts. Religious people put their non-religious guest on the spot by trying to get them to say grace. Even my own loss of faith was triggered by the fact that my parents suddenly wanted me to say grace. It wasn't that they wanted grace to be said, it's that they wanted me to do it, despite the fact that I didn't feel good about the idea. Desperate to be able to explain why I felt so strongly about not doing it (with adult vocabulary, I can articulate that the display of false piety made me feel hypocritical and rather dirty, and I was convinced that we would go to hell for trying to trick God by lying to Him, but as a kid I couldn't articulate this) I started thinking critically, long and hard, until I ultimately came to the realization that I'm an atheist.

So why do they want people who aren't interested in saying grace to say grace? If thanking the deity for the meal is so important, why aren't they eager to do it themselves? Why do they want to make their guests uncomfortable and have their deity get lied to rather than simply expressing their own genuine gratitude with quiet dignity in accordance with their faith?