The answer would be 'I don't really know why'!!!!!
I was experimenting with making it to offer as a class lesson should I apply to teach somewhere next year.
Making a pattern for my own enjoyment (or, should that be torture!) is a totally different thing to making (or should that word be designing?) one for a class.
Why? Well a class has a limited time slot and lots of people expect to finish a project within that class. Now this is almost impossible to design for as every student comes with different skill levels, different speeds of tatting etc so it's a bit of a guessing game for the teacher to get the pattern 'right'. My objective, too, is to get any new design element within the first half hour of the students arriving so they can get maximum benefit from the class.
The elephant failed my test!!! Well, for now he has and will be put aside.
While I was working HIM I thought of other ideas and, actually, while I'm typing this I've thought of another one!!!!