I'm guessing the biggest reason is that Ethan wants to shut down is that he doesn't want to deal with the stress of making sure the balances of all investors (BTC bankroll alone was > 100 BTC, or roughly 5 million USD at current rates) are safe. Continuing with altcoins likely wouldn't solve that issue, especially since ETH & LTC are fairly major coins too.
I agree with you on that, as i said, or tried to, the same reason just-dice switched from btc to clam, as i was told dooglus didnt wanted to take the responsiblity anymore so he switched to a coin with "much" less value, cause people did not want to see the site dying.
If not with ltc or eth, i think there are still altcoins (doge, polkadot, etc) which could be used instead, from what i understood most people love the community of the site and the gui and all other things around that, to abandon it completely would be disappointing, even it is all ethans decision.
cheers, whore-ray