You mean a regular side kick? I think side kicks may have been slightly disregarded because it's not exactly a solid knockout kick like the roundhouse. I think the side and front kicks are mostly seen as push kicks, since it's hard to end a fight with them unless you're very accurate. Mixed Martial Arts and fighting sports probably have contributed to this. In full contact sport fighting, you usually have a frontal stance towards your opponent, since that makes it easier to throw hard blows with your fists. In that stance a front kick is usually faster and more practical than a side kick, because it's thrown forwards. A sideways stance is good, because it's easier to protect your groin from kicks in that stance. This is one of the reasons why for an example Bruce Lee preferred this stance and also was famous for his side kicks, but since groin kicks usually aren't allowed in competition today, many people prefer a frontal stance to throw heavy boxing style punches and combinations instead. Concerning using the edge of the foot as a point of impact with the side kick, I think this is not stressed as much because the main target for that kind of kick is the throat (which is illegal in competition). Many people prefer to connect with the heel instead while side kicking to the body, since the heel is considered a harder and sturdier part of the foot.
With that middle knuckle punch I think it's much the same issue there. It's not a punch which is intended for pile driving impact power, but for very accurate strikes to very sensitive points on the body, which isn't considered quite as practical in a stressed situation, neither by full contact competition fighters nor by the newer generation of instructors of "real world" practical self defense.