Both planes are fairly old (24 years for the KLM, 15 for the one in Korea) so this is more likely a bad maintenance issue than an “omg Boeing quality control sucks recently” one.

I have no idea what your wall of text is supposed to imply or mean.

Isn't Boeing also involved in the maintenance part?

Not necessarily. Manufacturer recommends maintenance procedure but airlines can vary them, see American Airlines 191. https://en.m.wikipedia.org/wiki/American_Airlines_Flight_191

Both belly landing, but what a big difference it makes between having a completely unnecessary concrete-reinforced mound perfectly positioned at the end of the runway[0] vs not having such an obstacle.

[0] https://youtu.be/w1r8dl4RqMw?si=taZ5WmIcTH2ZGVci&t=187

Yeah that’s an odd one, barricades are usually only used if there is a risk of the aircraft going off the runway and hitting something that can actually have people in it like a building or a highway…

It’s not uncommon to have these at the end of the runway but it’s the first time I’ve seen one that seems to be solely to protect the ILS antennas…

I will correct myself I’ve seen arresting walls like this protecting non-human life endangering equipment on military runways where a loss of a single aircraft and either a single pilot or a crew can be less significant than the operational degradation of the airfield.

I actually wonder if there is some requirement in South Korea to harden civilian airfields due to their likely dual use in case of a conflict.