"Why?" - Just For You
Despite the wide range of microcontrollers available in the market, it’s unusual to find exactly what you’re looking for. This is because microcontroller manufacturers attempt to design their products to appeal to as broad a range of customers as possible, so their designs are always a compromise. In most cases, a microcontroller will be missing some key components and functions that a given design needs. Or a design team that was initially pleased to find a device that appeared to do everything they needed will discover that it consumes too much power or costs a lot more than they were expecting, because it also contains significant functionality their design does not require. Most design teams accept this situation and either build the additional necessary functionality onto their PCB in the form of additional devices and circuitry or live with higher costs/power.
Part of the reason for their acceptance is that the ideal alternative - creating their own perfect chip - is not something that seems realistic. Although most designers know about ASIC (Application Specific Integrated Circuit) design, they assume it would be too expensive or take too long.