A first aid kit has to be portable, and light weight enough to carry every time you head into the hills.
Bandages, splints, antiseptic cream, the list is almost endless, and so will be the increased bulk and possibly weigh.
When you try and include everything, then the size and weight of the kit, may get a bit too large.
Ive sprained my leg once over the years, and managed to get some shocking blisters, but i agree, unless your attempting a very long walk, Pennine Way, Coast to Coast, when you will need a more substantial kit, this tiny kit will suffice for most of us.