Ugh.
Depression is different from sadness. If your father died/girlfriend left you/job laid you off, you should be sad about events like those, and frankly, it would be concerning if you weren't.
The patients who are candidates for ECT aren't just upset. Some are actively trying to kill themselves. Others have such lassitude that they can't work up the energy[0] to eat, drink, or bathe, let alone live a normal life.
I take your point that the US tends to 'medicalize' conditions, and we might be better off with fewer drugs and a more caring society, but these patients aren't going to be helped by a box of tissues and a soft shoulder to cry on. It is an illness
[0] The suicide bit is not as contradictory as it sounds. Depression is associated with very decreased activity levels. Some depressed people make plans to self-harm, but lack the energy to actually go through with it. As they recover, the energy often comes back first, so they get into a regime where they are still considering self-harm but have also recovered enough to actually go through with it. As an analogy, think about the 'danger zone' in food preparation. Frozen or cooked food is relatively safe from bacteria, but during thawing, food is warm enough for bacteria to thrive, but not hot enough to eliminate them.