Why isn't Sona picked in the lcs?

Because she's the balance team's punching bag.

Her strength lies in her teamfight utility, which is why her winrate keeps going back up after each nerf. But the latest one was so heavy handed (including mana regen nerfs) that now she simply can't survive long enough to do anything at all. If you so much as breathe on her she dies, and she has no mobility and no peel outside of her ultimate.

if she picked and won an LCS match then she will get nerfed again

Slow movespeed Weak endgame Easy to gank Hard for teammates to gank for

Pretty much those.

The pros probably prefer using supports with hard CC available more frequently than once every 60 seconds at max CDR.

• Squishy
• Easy to get ganked
• Not much disengaging move on an 8 sec cooldown like Janna's.
• Dat fking 200 mana ult at max rank

She received quite a few crippling nerfs during her life time, pre and post rework if I am not wrong.

I would imagine the last straw was the mana regen nerf since she relies quite heavily on that too.