This is hardly above the nebulous drivel of the articles that popped up during the week of the flood, just dressed up with a professional veneer. It manages to sneak in a clickbait headline, and despite the promise, you don't get to find out the cause, just three contributing theories. Also, did you know dams are bad?
The terrain in these Himalayan states is rough. Steep river valleys, no flat land, and towns clinging to cliffsides. They're vulnerable to floods every day. If anything, dams alter the risk profile dramatically, increasing the impact of the rarest of floods but greatly reducing their frequency. And, they generate soot-free, low-carbon electricity from these rivers that are hardly ecological havens: they're the upper tributaries of some of the most polluted rivers on the planet.
Altering the natural environment is always a trade-off we should examine and justify. But in this instance, they add up. Without the dams, an identical flood would've resulted in at least as many casualties, and that will continue to be the case until you build even bigger dams whose reservoirs provide more cushion against freak floods, melt, and landslides, and/or until you banish people from their homes in towns that dot these deep gorges at a great socioeconomic cost.
The environmental risks are an inseparable part of the region. You can't wish the possibility of all landslides away, the glaciers can misbehave as long as they exist (and we want them to exist), and the topography and the settlement patterns will remain vulnerable to floods. Only abandonment, damming, or relocating the towns to flattened ridgelines stand a chance to improve outcomes for its people, and all of these come at high cost and involve major trade-offs.