51% attacks aren't just a single actor dictating blocks, but the threat of a cartel of large stakeholders cooperating to attain 51% of vote power
It's also not really a scenario worth considering.
In order to cooperate, the miners/validators need to have full alignment on their goals. Which is very unlikely for Sybil attacks, which almost always destroy systemic economic value — including the value held by the attackers. You might be able to find e.g. a government who wants to do a Sybil attack to accomplish goal X, and are willing to burn down $N billion dollars of their own staked assets to do so; but can you find a bunch of other governments or large corporations who also want to accomplish that same goal X more than they want their own stake-value? And who can be trusted to coordinate and not leak the plan?
A Sybil attack is basically like a bank heist where the attacker(s) have to pull up to the bank in their own personal aircraft carriers (destroying said aircraft carriers in the process, from the hull damage of sliding along several city streets), without anyone realizing they're coming. You can maybe theoretically do it as one entity with full internal goal-alignment. It's much harder to do it as multiple entities.
> 1.4. Governance and Voting. For certain Digital Assets, the underlying protocols offer stakers the ability to vote on matters related to the governance of protocol-level issues. Coinbase may or may not support voting for such assets, and may cease supporting voting at any time in its discretion. Coinbase will comply with your instruction to vote your Supported Digital Assets to the extent Coinbase or its affiliate supports voting for such Supported Digital Assets. In certain cases, Coinbase may vote on your behalf where Coinbase or the applicable protocol does not support delegated voting; in those instances, Coinbase will vote with the protocol’s recommendation.
But what about jurisdictions that compel them to vote in certain ways?
From the Coinbase page on Eth2 staking (https://help.coinbase.com/en/coinbase/trading-and-funding/co...):
> To be eligible to stake ETH, you must: [...] Live in a jurisdiction eligible for ETH staking.
> Which regions are eligible for ETH staking? [...] United States (excluding Hawaii & New York)
In other words: they're just not going to offer the service in any place that compels them to vote a certain way.
I presume most delegatable validators have chosen a similar option: avoiding the problem entirely by not taking anyone's money if they're from those jurisdictions. Just as most ICOs in 2017, when the US didn't have regulatory clarity on crypto being a security or not, just avoided the problem entirely by preventing (direct) sales to US-market investors.