I imagine it's because BartPE didn't support anything after XP/Server 2003 so continuing to support/maintain it would be a waste of time. The issue I see with tools like these is the questionable/unclear nature of using/distributing disks created with these in terms of the Microsoft EULA. I've therefore always been uncomfortable using Windows based "rescue CDs", especially in a commercial environment. From what I've found, there's been no time I can remember where a Linux/UNIX/DOS based recovery live CD has been insufficient, and those tend to not have the licencing issues that Windows based ones do.