A professional wrestler can get over in a number of different ways. For the likes of AJ Styles, their popularity stems from the strength of their ring work, and for others, like Hulk Hogan, it's their magnetic charisma and showmanship.
Some do it with their company's full support (Triple H), while others get there in spite of the bookers' actions (Daniel Bryan). Whatever the case, getting over is never easy, and maintaining heat is even harder.
One of the modern WWE product's biggest failings has been its complete inability to establish and sustain stars comparable to those forged in bygone eras. The current roster isn't totally devoid of star power, but wrestlers just aren't getting over like they used to, with much of it down to the performers and the way they've been presented.
The current talent pool is flooded with wrestlers that fans just don't care about, because they haven't been given a reason to do so. It's both the performers' and the company's job to build a level of investment, but they've failed. Badly.
Some of these wrestlers may eventually recover, but for now, their popularity has either stalled, or is stuck on a steep downward trajectory.