NEW items that are just a tease

I visited SA in Feb 2024 and was pleasantly surprised to find that Mugg & Bean had a new dairy free coconut milkshake on offer. I ordered one at Cape Town international airport but to my dismay they said "they didn't have the ingredients to make it", keeping in mind that there is a Woolworths food downstairs where you can buy a can of coconut milk pretty easily. Fast forward to August 2024 (a whopping 6 months later) I come back to SA to visit again and try my luck once again with the NEW menu item at the same location. Again, the same excuse. My question is why have something on your menu that you clearly cannot offer the customer? and how long does it take to stock up on ingredients? I emailed Mugg & Bean customer care - and no surprise here - I had zero response from them. Considering everything is overpriced anyway, it would be nice to acknowledge the customers you still have (had)!