This is because universal design features are easy to access and use, require little physical effort, and do not have to be used in just a certain way (flexibility and tolerance for error). A rocker light switch is a classic example of universal design because it can be operated by touching the control near the center or more toward the edges. It can be turned on or off with just a finger, a closed fist, the back of the hand, an elbow, shoulder, or even something being held and then used to touch and operate the switch. It can be used with a kitchen mitt or with cold weather gloves or mittens. It is universal.
Contrast the example of the rocker light switch with the older-style toggle light switch (the one with the little protrusion that must be pushed up or down or grasped to move it). It's also possible to create a little discomfort in one's hand if the contact with the switch is a little forceful or haphazard. True, the switch can be turned on or off by brushing or leaning against it (mostly accidentally) or managing to move the toggle with the elbow, edge of the hand, or shoulder, but this is not how it has been designed for use.
Another key property of universal design is that it is essentially invisible as any type of prescriptive treatment. If a toggle light switch doesn't work well in someone's home environment, for instance (in keeping with the previous example), replacing it with a rocker switch does not carry any type unusual response from people. They are surprised, taken aback, or otherwise remarking about this type of treatment except perhaps to compliment the use of it. It just fits in.
Many people have begun turning to technology in their homes, when that may be the only type of improvements they are making. They aren't addressing mobility, accessibility, or safety concerns, but they like the idea of using their cell phone, tablet, or digital controls to regulate their lights, temperature, appliances, or front door locks. They like wifi and blue tooth applications.
As great as these applications are, they aren't the total package. Universal design is more than technology. Some home builders have begun installing wifi and blue tooth applications in their homes. These are fine as far as they go, but there is considerable room for growth in presenting universal design elements to the marketplace.
Technology is appreciated by consumers and readily identified by anyone entering their home. The convenience it offers is unmistakable, and it is a wonderful universal design element. However, there are so many other universal design elements that can be included in a new or existing home that allow people to use their homes more effectively and safely.
In addition to thermostats, door locks, window and lighting controls, water temperature and flow rates, appliance settings and management, and responsiveness from devices like Ring, Next, and Alexa, there are many design elements that can included in a home to improve footing, entrances, passageways, seating, and general safety that can get overlooked if the emphasis centers on the technology aspect. Technology is fun to see and use. We like it. Nevertheless, it is a more obvious addition to a home than other universal design features that are more true to their core concept of fitting in without any particular notice.