If Riot Games hates Soraka, what do they think of Janna

Not sure why you think they hate Soraka...

Anyways, in general the sentiment (at least from Riot) is that heals are unhealthy game play while shields are healthy game play.

Heals require no timing skill and simply recover an ally who messed up. No enemy enjoys watching someone they just outplayed and put significant damage on just shrug it all off as they get healed back to full. Shields require more skill. The shielding champion has to be present when the damage is being applied (not run there a couple seconds later). The shield needs to be applied before the damage gets applied, etc...

Now, with how long shields last (anything over 1 second really defeats the argument above in my opinion, and they're ALL over 1 second), how heals have alternative counterplay (% health damage is stronger against heals, and there are grievous wounds), and how shields really block way too much (e.g. they effectively block true damage since they selectively block everything else, it would be healthier if true damage ate up the shield AND applied damage to the champion...), etc... I don't really agree with Riot. I think shields are honestly OP. Shield comps are disgusting - put two strong shielders on the same team and it becomes almost impossible to kill their carries with the level of coordination in solo queue.

Raka is the healer, and janna is the peeler, both filling those niches reasonably well but not necessarily offering much else, which I don't think riot necessarily hates, despite some portions of the community hating those two for doing their respective jobs well 'easily'.

That said, raka is probably tricky to balance due to grievous wounds being a thing, so she's quite powerful when people aren't building it, and somewhat less powerful when they are.

Why don't they just delete Soraka from the game

I hate Soraka and love Janna. They are two very different supports.

Raka: somewhat aggressive with poke, out-of-combat ally buffing, high range. Janna: least aggressive, only in-combat peel, ridiculously low range.