They’re just not.
You see “RPG elements” on the back of game-boxes for assorted games, frequently tactical combat games, or mentioned in game reviews. The thing is, that what they’re referring to as RPG elements aren’t actually RPG elements.
The things they’re generally describing are classes, levels, abilities and experience points. Units or characters that get stronger and/or more versatile with experience. Those are what we used to call wargaming elements.
You see, role-playing games (as we know them) are founded in Dungeons and Dragons, developed by Gygax and Arneson from Gygax’s Chainmail medieval miniatures wargame rules, which in turn were based on wargames of the day. Most wargames designed for anything more than one-shot battles have classes, levels, characters, abilities and experience points after one fashion or another, because that encapsulates some of the realities of armies.
RPG elements are everything else. It’s reasonable to say that if you think “Miniatures wargame elements” everywhere you see the marketing term “RPG elements” you’ve pretty much got it right. If you’re thinking about genuine RPG-elements, you’ll generally find none of those at all in any game which actually advertises them.