I have a question, why is Kayle being played so frequently now?
As someone who's played since beta, Kayle's play pattern has looked like this:
Riot changes items around. Kayle abuses the items and becomes a top-tier champion. Riot nerfs Kayle. All of Kayle's fanboys get really butthurt and stop playing her. Riot changes items around. Kayle abuses the items and becomes a top-tier champion. Riot nerfs Kayle. All of Kayle's fanboys get really butthurt and stop playing her. Riot changes items around...
Kayle has risen out of nowhere and become a top-tier pick more than anyone else. She does it about every 9 months.
Kayle's kit is also objectively OP in just how it does things and what kind of flexibility it offers her.
Kayle has been played competitively as a top-lanner, jungler, mid-lanner, and support. Can't be said for anyone else. In most cases she also builds the same thing each time rather than needing to change her build like several other flex-picks do, effectively making Kayle a 4-for-1 deal. Considering Kayle's play-style is actually a lot like a marksman, more 5-for-1.
Pretty impressive considering most other flex-picks tend towards the Lulu/Nidalee style of having 7 abilities rather than 4. Kayle just has 4 really solid, multipurpose, very fluid, and extremely solid skills.
Kayle can also use pretty much every item in the game, giving her a lot more chances to abuse itemization than anyone else. Even with items that are objectively terrible on anyone not named Kayle, as was the case with Nashor's Tooth and later Hurricane giving Kayle the power-spike she needed.
And Kayle is a pain in the butt to counter-build and kill: while most glass-cannons go squish and get hit with a double-whammy from defensive item.
Marksman's physical auto-attacks are hit twice by most armor items: 
, mages magical abilities are hit by a double-whammy from most MR items 
, Kayle's magical-auto attacks are generally going to hurt regardless of what you build: and then they'll really hurt when her passive shreds those items.
Not to mention Kayle's Righteous Fury gives her a rock-solid early game with great steroided-up dueling potential and wave-clear, her AP QWE burst from bases has generally given her a rock-solid mid game, and her impressive scaling and extremely powerful ult have tended to give her a really great end-game phase.
Kayle does have her downsides, but it's pretty difficult to imagine her ever being a bad champion or Riot actually nerffing her enough to be unable to use her considerable strengths to wind up being a top pick over and over again.
Now there's also 
breaking the power-level of a lot of champions, and that item was pretty solid on Kayle when it was complete garbage on everyone else.
