Hell nope

This is an example of sound change, and there are a few hypotheses we can consider as to why this sound change came about.

The first hypothesis is that this is the result of sound change through misperception. No, particularly when said in isolation, and abruptly, ends in a glottal stop: You can feel your glottis (vocal chords) closing, if you pay attention. Glottal stop is easily confusable with the standard English sounds p, t and k. When you combine this with the rounding of the lips from the o sound, you get something more p-like versus k-like. (Note the position of the lips w/ a p; in contrast, many languages had glottal stop ~ k sound changes, e.g., Hawaiian).

This results in acoustic cues at the end of no that make it sound like maybe possibly there is a p at the end. Some people misperceive that as a full-on p then start purposefully adding the p and the rest is history(cal linguistics).

More generally, it's likely incorrect to presume that language has an explicit drive toward being easier. Rather, there are tangible forces at play that result in it generally being easier, but not always (e.g., nope).

Plus other theories equally as dense. I use "nope" (I think) because it somehow seems to soften the sense of rejection. "No" is just cold and formal. "Nope" sounds like a buddy rejecting you reluctantlyand regretfully.