Part of it, certainly, was that I enjoy participating in other people's religious celebrations, even though I'm not particularly religious myself.
Another big part, though, was that I got a chance to flex my Boy Scout skills. I really enjoyed knot-tying and lashings as a Boy Scout, and those lashing skills haven't come into play that much in the last decade.
So I taught Monica square lashings, clove hitches, timber hitches, and so forth, and we built the frame and lashed the wooden trellis to it with twine. I did wax a bit didactic in this--I even found some nice demonstrations of the usefulness of frapping.
The resulting structure looked very neatly and tidily built, if I do say so myself. I felt pleased.