Some of us have past experience with this patient population, either through past jobs or through personal past injuries or whatever. Other than that maybe you can just realize that the feet are our means of mobility and one of our primary interfaces with the outside world, so the role of the foot/ankle is vital. Furthermore, since the feet are at the extreme end of the circulatory and nervous systems, those types of diseases are likely to impact the feet and since they are well below the majority of our body mass they are very likely to suffer from weight bearing or overuse injuries. For these and other reasons you can see why there has always been (even back to ancient times) a need for dedicated foot care. Whatever you tell them, you should make it clear that you understand why a dedicated foot/ankle specialist is necessary or why you are interested in the foot/ankle.
Furthermore, as for why you would choose DPM vs MD/DO foot/ankle specialist, I explained that not very far back on this thread and you can find my source on that post if you're interested. To summarise it, if you already know that you are interested in foot/ankle from the start (previous paragraph) then there is absolutely no reason why you should choose MD/DO. As a pod you will be exposed to more foot/ankle specific pathology throughout school and then in residency you will see over 1000 foot/ankle procedures whereas the average for an MD orthopedic 5 year residency is around 200 foot/ankle procedures, or 40 per year. Then the MD would do a 6 month to 1 year dedicated foot/ankle fellowship. By the end of this they'll of course be a full orthopedist with some specialty in the foot but nowhere near as much education or experience about the foot as we would have. Plus they'll only be able to treat musculoskeletal diseases/disorders of the foot whereas we could do derm/neuro/infectious diseases/wound care/etc of the foot/ankle. I think if foot/ankle is what you wanna do then overall quantity and breadth of education and exposure to the foot and ankle is infinitely more valuable than whatever letters might be after your name. You'll be more capable and confident in the treatment of your patient's foot/ankle conditions.
You probably shouldn't straight up say that you just want an easy route to surgery or you want an easier lifestyle because they might see you as lazy. You should probably also not say because pod school is easier to get into.