Coins just don't go up like that. There needs to be a solid reason. Bitcoin prices have gone up, as a result of the hype surrounding integration into platforms such as PayPal and Square. Some of the altcoins have also gone up, mainly because they are also traded against BTC. Their exchange rate versus BTC has gone down, but that against fiat has gone up. But this trend is not going to last much longer and the hints are already there. Bitcoin dominance now stands at 72%. It was 57% before the start of the bull run.
Altcoins follow the Bitcoin's bullish trend at the moment (at least some of them). But I agree with you, the trend may not last long. Bitcoin is probably still the safest to invest in the long run.