Tiramisu - Why is it so hard to get?

Another dinner at the local Italian food place. Again I asked for Tiramisu (which is on their regular menu), and they didn't have it. This would make it a total 12% availability of Tiramisu over the last year. Every time I go to this place (which is quite frequent), I ask for Tiramisu - and still they don't bother regularly preparing one.

And it's not even only at that place. It's almost the same with all Italian restaurants, judging by my past experience. Why don't they get it? They won't sell anything by just putting it on the menu - they actually need to have it available. *sigh*.