When you take a look at what Link has to go through, I can see reason in why they're giving him pants, or at least something that looks like pants.
Hailing back to the old games, you see the classic, iconic, green tunic, an amazing choice of style unlike any character design of the time. Drawing up images regarding the Heroes of Old, Link himself sees reason in donning the clothes worn by his ancestors. This canonical reason is given in pretty much every single LoZ game to date. It helps connect you with the games across the series, as well as being an easy eye opener for people who are playing the game for the first time.
Now, I can see where people might have a difficult time accepting change regarding Link's attire, but let me ask you a question. Do you really want your hero to be clad in super sexy get ups that offer him absolutely no protection against the danger he faces?
Point being why I think they're shying away from the idea of "tights", and looking for a more logical decision for his leggings. He's a tough guy, he's jumping, falling, dashing, dodging, and pretty much ripping things apart within the first hour of his adventure. He needs to have something that will protect him against the elements, be it monsters, weather, or grass stains.
Character design for an iconic figure like Link is difficult. Nintendo and it's developers have to do it justice, but they still want the admiration from us, the fans. Taking a look at the current concept art, I agree, it does look a bit incomplete, or maybe it's simple for a reason. Like I stated before, it has it's usefulness as well as its purpose. An amazing topic of discussion, I think we'll be able to look forward to what kind of choices Link will make regarding his pants for the future games, Lmao. I'm just not expecting him to run around for an entire game in a suit of armor, because that would be silly.