While it does seem like the same skill, there are some unique challenges that come with both. Punts and kickoffs are NOT the same!

Unless there is a penalty, kickoffs always take place from the same distance and the kicking team can't cross the Line of Scrimmage until the ball is kicked. It's harder for the kicker to do much with the ball as well. They usually just try to kick to a certain side of the field and try to kick a touchback.

The kickoff returner has less decisions to make as well. They must field the ball as it is live once kicked (unless they are sure it will bounce into the end zone). They also have much more space to work with as it takes longer for the kick coverage to get there.

Punts are totally different. They can take place at any yard line and the punter has WAY more control over the ball. Punters have much more control over the placement and ball movement. As such, punt returners are usually guys with good hands. Also, the punt coverage team can leave the Line of Scrimmage as soon as the ball is snapped. Combine that with a punt that may be kicked from a shorter distance with longer hang time, the punt coverage team is usually on the punt returner before the ball gets there. A punt returner has to judge how the coverage is coming, where the ball is going to land, how it's spinning, etc. They also have to gauge if they should fiar catch the ball, let it drop and roll or catch and return it.

Much like punting and kicking AND the regular Center vs the Long Snapper, these positions seem very similar, but they are not. There are guys who can do both, but teams like to have a specialist for each situation.

When returning a kickoff, there's usually a good 15+ yards between you and the nearest defender, so you don't need to worry at all about immediate contact. Your job is to catch it and then get up to speed as quickly as possible and then read your blocks and find the hole.

I.e. KRs are about top speed, thus long strides, straight-line speed.

Punt returners often have guys within 5 yards of them, and since the returner is stationary to catch the ball, and there are guys flying towards them at full speed, they rarely have the luxury of catching and then getting 10 yards of open space to get up to speed. Instead they need to make people miss almost immediately, and they have to do it without being up to speed, instead it's more about low-speed jukes, spin moves, etc.

I.e. PRs are about acceleration and change of direction, making people miss, and not as much about straight line speed.

This is why kick returners are often taller, longer legged, track-star types. Punt returners are often small, shorter, more elusive guys that can change direction more quickly but maybe don't have that super high-end speed.