You move up to ensure that you get him, it's really that simple. After the combine Love is the top two or three players in the draft, it's a position of need for KC. Why would you not give up a 3rd pick to get such a player?
You do not worry about 4 years down the road, if he is as good as everyone says he is, then you pay him and get a decade out of him and Mahomes together. KC is not going to have a chance to get a difference maker on offensive anytime soon most likely, you have to grab a generational player at a position of need if you can. It was a mistake not giving the Jets what they wanted for Hall, either a 2nd or 3rd round pick, now they have franchise tagged him and he is off the market, let's not make the same mistake and miss out on Love.
Hell if KC would have had to give up their #40 pick to the Jets and signed Hall they would be in a better position now that what they currently are, with #9 and #29 to take on defense. They blew that opportunity, lets to do it again.