They are for cars.

The strength requirements are similar to the US standard (resistance to point loads of 50kN at 1/8th of the horizontal member from the outside, 100kN at the centerline, and 50kN at 355~635mm from the centerline), but the EU has mandated front and side guards (as well as back which the US also mandates) since 1994.

Of note: a 2012 IIHS study indicated that only 15% of collisions between cars and large trucks were rear collisions , 22% are to the side of the truck, and 63 to the front.

Yep. When they have bars, these bars are precisely meant to stop a car or motor bike from sliding under.

Bicyclists have way less momentum, so sliding under would be less of a risk, I think. They experience plenty of other risks though.

The side bars can help push a cyclist away from the vehicle if they collide with it while its turning.

Those hold cars. Up to a degree of course.

They only need to slow and control the car's stop so that it doesn't slip under too far. In this case there is no perfect, but a massive improvement in safety in just three box steel sections should be a very palatable regulation. Apparently it is too much to ask.