Because it is a non-argument. The implication is that engineers are incompetent and will never gain competence. There's much more detailed arguments to be made, but I'll give you two things to consider that will give you context and help you track down those arguments if you are interested

1) RBMK reactors (like Chernobyl) have a positive void coefficient, which leads to an increase in radiation as steam pressure increases. At the time of the of the disaster, this was generally considered "not a good idea" due to the ability for these reactors to explode and release high amounts of radiation. This was even known by Soviet Scientists and was even a plotline in the HBO miniseries (people seemed to miss this, but maybe a priori knowledge made it more significant to me).

2) Concerning Fukushima, the region was hit with the largest tsunami ever seen in recorded history for the area and one of the largest ever recorded anywhere. Meaning the largest to hit Japan in at least 1000 year. With the reactor being built in a time where scientific knowledge did not know that this magnitude of an earthquake was possible in such a fault. The comment implies that such lack of knowledge, and thus potential for danger, will always exist. But the knowledge even advanced before the quake happened, but was still relatively new at the time (btw, this also applies to the Cascadia subduction zone off of Washington and Oregon).

These were due to two completely different causes, with 25 years of experience between them, and with the latter being caused by an extremely rare natural disaster. It is improper to characterize risk by black swan events (or gray swan events, which may be more accurate concerning Fukushima). Additionally, the results and causes are not even remotely similar. The connections are simply that both involve nuclear power. It is literally comparing apples to oranges, which both happen to be round fruit that grow on trees. The argument is setting an impossible standard and using a false narrative. It is posting with high confidence but low expertise. In the end, it only confuses and makes it more difficult for anyone reading to acquire accurate knowledge about the events and actual risks of nuclear energy.