Minimum amount needed to stake: This determines the barrier to entry.A minimum of 32 ETH is required, and people can only stake in 32 ETH multiples.
Delegation: Can stakers outsource the work of running the physical validator node, or do they have to do it themselves? If delegation is impossible, hardware and bandwidth requirements can prevent some people from staking.
There is no in-protocol way to delegate stake to other validators.
Lockup: How long does it take to withdraw staked funds? Longer lockups tend to increase the security of the protocol, but also make it less attractive for stakers due to lower flexibility and higher opportunity costs.
Today, stakers cannot withdraw ETH from the Beacon Chain at all. After withdrawals have been enabled, the lockup period for unstaking will be 27 hours.
Returns: How much do stakers earn over time? The higher the returns, the more people will stake, leading to higher security.
Stakers on the Beacon Chain currently earn inflation rewards. After the merge, they will also earn transaction fees and MEV. The inflation rewards depend on how much ETH is currently staked. More staked ETH implies less inflation rewards per validator and vice-versa. Today ~4m ETH is staked, leading to an annual return of 7.8%.