Often a combination . Many celebs have multiple tightening procedures coupled with many fillers and Botox uses. They demand a very tight pull on lifting, which may produce the unnatural look you see. Often surgeons are urged to tighten too much, when use of fat grafting to cheek areas revive the middle third of face, improving the natural, youthful appearance better than over tightening. Aging is 3 dimensional.
Technique dependent. Although it may be a result of too many procedures, if the surgeon does not use a technique that pulls the skin too tightly on the first surgery, one's natural features may be distorted and lead to an unnatural appearance. Always look at the before and after pictures at the surgeon's office to see what previous patients' results have been.
Often. Or perhaps their plastic surgeons yielding to pressure to "pull it really tight" coming from the celebrity, themselves.
Could be & much more. It is likely due to that as well as lasers, fillers, botox, peels, etc.
Some & In part.
Depends. There are many that have unusual changes to their appearances, sometimes after only one treatment. Varies with patient desires and surgeon's preferences. Most prefer the natural look, which is best if you can't tell they've done anything. All want improvement of skin sagging, but most don't want to look like freaks.
Facelift. It could be a revision facelift but it could be a primary too.
Sometimes. These problems are commonly multifactorial, involving surgery, lasers, and injectable therapy.
Can be. Or fourth or fifth! too much facial plastic surgery is discouraged. Your doctor will suggest alternative treatments like facial fillers to avoid the over tightened look.
Possibly. Many older celebrities had facelifts using older skin-only facelifts. A properly done facelift now days results in a natural look, even after repeation two or three times.