Hash rate goes up, difficulty goes up, less coins to mine. When the value of the coins mined over 24h result in less value of mining LTC straight, then it makes no sense to mine Karma. For a miner like me, it's attractive to mine a coin that maintains high value vs LTC.
So the questions becomes, where can we find a sweet spot where amount mined over 24h still makes more vs LTC
The advantage that you have when mining Karma over LTC, is that you have a MUCH higher probability that Karm price will increase a lot in future.
The issue is you can mine the most profitable coin and then convert it into Karma (and effectively mine MORE Karma). So that theory doesn't really hold up.