That is part of what makes Mt. Washington such a hazard. It doesn't look like a very serious climb, and due to its location in a popular vacation area it attracts visitors who don't have much, or any experience in mountain climbing or even serious hiking. They haven't taken the kind of training they should have, and are un-prepared.
And then the weather changes on them. The hike up seems fine, with pleasant summer conditions until all of a sudden you are above the tree line and it goes from a pleasant day to 32 degrees with freezing rain and a ninety mile an hour wind. And then the snow arrives - not nice light powdery stuff but wet gloppy snow that sticks to you. And then you can't see more than a few feet in front of you, the rocks are slippery, and you can't see any of the trail markers.
That's when the proper equipment and knowledge is essential. And even then Mt. Washington can snare experienced and prepared hikers. Few people appreciate just how high the wind speeds can go, and unless they have serious climbing experience few hikers can make much headway at all when the wind is strong enough that they can no longer stand up.
Mt. Washington and the Presidentials are a great place to hike and climb, but as you noted make sure you have the essential hiking gear, proper clothing, and at least some mountain survival skills. And watch the weather and be ready to turn around and head back down even if you planned to something else.
It can be as simple as carrying one of those $5 mylar bags in your pack. Those will cut the wind and keep you from freezing. I keep those in our vehicles for emergencies.
In summer in the Utah desert I frequently see hikers carrying nothing more than a small water bottle. That’s just asking for trouble