Can you explain to me why Ubuntu permitted Windows have bash inside that OS? What is the reason you gave bash to Windows?
It was Canonical that made that arrangement, not the Ubuntu users on this site. I'm just a guy who uses Ubuntu; I have absolutely no connection to Canonical or this project, and I imagine most people on here are in a similar situation.
However, Canonical developer Dustin Kirkland wrote the following on his blog post announcing the Ubuntu Bash shell on Windows:
Finally, I imagine some of you -- long time Windows and Ubuntu users alike -- are still wondering, perhaps, "Why?!?" Having dedicated most of the past two decades of my career to free and open source software, this is an almost surreal endorsement by Microsoft on the importance of open source to developers. Indeed, what a fantastic opportunity to bridge the world of free and open source technology directly into any Windows 10 desktop on the planet. And what a wonderful vector into learning and using more Ubuntu and Linux in public clouds like Azure. From Microsoft's perspective, a variety of surveys and user studies have pointed to bash and Linux tools -- very specifically, Ubuntu -- be available in Windows, and without resource-heavy full virtualization.
In other words,it makes Windows 10 more attractive to developers, and gives Ubuntu a wider audience. Of course, different people will have different perspectives on who benefits more from the arrangement and what its possible side-effects might be down the road, but it's a mutually beneficial arrangement.