It didn't exist when Arduino started their SAMD boards line. There's always a new chip coming out. Slapping one on a PCB is the easy part. Software and community support is the hard part. That support is much more desirable to Arduino users over features. So it makes sense to pick a chip and then stick with that chip until it's obviously outdated.
Arduino made an excellent decision to focus only on a few popular AVR chips for years. Look at what happened with the Primo. .org decided to just slap a new chip on a board but didn't bother with the support side of things and you never see anyone using that thing. There is only a limited amount of resources for development. Make the existing products work well or churn out new boards and ignore the problems with the old ones. Take your pick. I think Arduino is making a huge mistake with all these new boards when there are so many previous projects unfinished.