Vitalik decided to switch to POS due to their competitors scalability. But I think the reason it was taking too long is because its very hard to make this transition and ethereum had very large data in it. So transition from POW to POS is really hard though they are working hard,lets see if they can do it.
I have read a thread with also discusses the transition of ETH but what I have read as that ETH will not really be going int full POS but this is going to be hybrid POW and POS combined. So the main reason is for the scalability which I think its really important to address since the time where the kittens were active the network is clogged and gas price goes high. Its almost bullrun and halving is also few month later so its very timely and ETH will sure stay on the 2nd cap rank still.
