Why Are Smaller PoW Cryptocurrencies More Susceptible to a 51% Attack than Bitcoin?

Smaller PoW cryptocurrencies have a significantly lower total network hash rate compared to Bitcoin. This lower hash rate means the economic cost and computational power required to gain 51% control are much lower and more attainable for a potential attacker.

An attacker can often rent the necessary hashing power from a mining pool or cloud mining service, making the attack financially viable.