EXACTLY. One simply needs to send a text (or CALL *gasp*) and say something to the affect of “I had fun on our date/texting you for the past few weeks (or whatever), but I don’t think I’m into you enough to start a relationship. Good luck in the future.” The end. Then, not only is it cleared up that they are just not into you (and not on a vacation somewhere with no cell service or any other myriad of excuses), but you do not view them as being a rude person — just honest.
-From an almost-30 millennial.