Skins from a business standpoint

So skins are a pretty hot topic right now, and a lot of us are upset over the release of yet more skins for the same groups of popular champions while our favorites collect dust.

And thinking about it I had a sudden question pop into my head... Why is it that skins are more profitable on popular champions?

I would think that producing skins for champions that have low play-rate might draw more people to want those champions, and thus they would spend IP / RP to get that champion and then some RP to get that skin for that champion... Essentially it would actually increase spending and diversity in the game, as people would attempt to fill out their rosters with champions that they might have otherwise not found cool enough to get. That's my theory anyway.

And even if people spend IP on the champion, it does 'drain' their IP so that they are more likely to spend RP next time content gets released (Wasn't this discussed when talking about how Runes that cost IP still served to earn profit for the company because people spent their IP on the runes and then needed RP to get champions?)

I'm genuinely curious about this. Thoughts?