Microsoft Claws Back eBooks

Microsoft's eBook store: When this closes, your books disappear too    Article at the BBC.

After MS's abysmal performance with a series of launch-and-flop music "services" which left people with unplayable music libraries, why would anyone expect anything different of that company when it comes to books?  At least they're buying the titles back from customers this time.

Now having said that, I am fond of my Kindle but I only treat it as a convenience.  In principle, this same clawback could happen with Amazon too, and probably without the buy-back simply because of the vast number of titles they've sold.  This is why anything important should be bought IRL, and preferably at a small bookstore sporting a few cats.

But overall I don't get it.  Why disable books on e-readers?  Why not just leave them as useable orphan devices?  More to the point, why would anyone trust Microsoft with their book library?