Several reasons:
- Altcoins always tend to be much more volatile, and they exaggerate up- and downswings.
- The "dominance" value isn't calculated correctly, as it mixes apples (coins) and oranges (tokens). Tokens are a completely different asset class and intrinsically much more volatile than "coins" which are meant to be used as currencies. Tokens only appeared massively last year, leading to the "dominance" decrease, and now are "back to normal".

- Most of "tokens" are worthless crap without any use case. Now that even the most stubborn bull has recognized we are in a bear market, there is not a single reason to hold them.
- ETH losing momentum since a couple of weeks - also here, fans are slowly capitulating.
But it is not the "safest alternative", it is the only cryptocurrency to hold in bear markets, or for me, the only cryptocurrency to hold for store of value in any type of market condition. Although, I have a small "investment" in Decred. Hahaha.
Decred really seems to be pretty stable (73% down from ATH), maybe its "ticket" system is stabilizing it a bit. Other stable currencies (not tokens):
- ZenCash (-73%)
- Stellar (-77%)
- ETC (-77%)
All others, including Ethereum, lost more than 80% since their ATH.
Source:
https://onchainfx.com/