Cool but most of those have tab.
I can maybe shed light on that. I wrote a book for Alfred Music. It was a mandatory publisher's requirement that my book include TAB. The rationale is that you can sell more books if you market to both people who read notation and people who read TAB. I suspect (but don't know for a fact) that Hal Leonard also requires their authors to use TAB.
Sidenote that it was actually a good learning experience for me. When I sat down to write my book, I didn't know how to read or write TAB, and had to figure it out in a hurry. It's not a skill I use frequently, but I'd still rather have more skill than less skill as a well-rounded musician.