Looking at the lore of Syndra and Zyra it is very confusing as to why beings who prize freedom over everything else and who have only recently obtained there freedom would consent to have their bodies and powers bent to a summoners will in order to compete in the League of Legends...any thoughts concerning this?

honestly if i were zyra (and then i would do unspeakable things to myself) and i just tentacled my way into some random summoner (who happens to be very um, physically endowed), i'd really have no idea where the heck to go. might as well go to the league lol

A better question would be why so many champions bent on revenge would join the league, knowing that it would mean they could never actually kill the one they're after.

Because killing them once isn't enough.

Also, I suppose they want to humiliate them as much they can.

Syndra is probably doing it to gain political influence, much easier to take over the world or whatever shes planning if shes got enough IP to just make whoever would try to stop her look the other way

I don't think Syndra's the type to take the roundabout way of destroying people...

Just ask her mentor.

I would think syndra would join to strengthen her powers. After all the champions would likely be the ones to try and stop her