The gist is that Portland drivers couldn’t stop hitting crucial safety infrastructure (proving its necessity) so PBOT gave up on it.
As one of the commenters pointed out: Since a pedestrian/bike fatality costs PBOT nothing and replacing a concrete planter a car has demolished costs them more than nothing, to balance the budget they’re going to go with more pedestrian deaths.
Not every intersection should or needs to be replaced by a roundabout, especially on local lane intersections where speeds are already supposed to be low. They take up more space, are more expensive to maintain (than a stop sign-controlled or uncontrolled intersection), and are also less convenient for bikers as well as cars.