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.

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.

Those hold cars. Up to a degree of course.