Recently, I learned about the concept of the 51% attack which a malicious actor could perform on a cryptocurrency. Essentially, if you can control >50% of the hashing power for a given cryptocurrency, you can control the blockchain which allows you to do all sorts of devious things like double-spending the cryptocurrency.
There's even a website, crypto51.app, which keeps track of the theoretical costs of performing such an attack. This cost seems to come from the money one would spend in gaining that >50% control for an hour - usually in terms of renting computing time.
Clearly, the more computing power the cryptocurrency community is putting into mining, for a given cryptocurrency, the harder and more expensive it is to perform a 51% attack. So crypocurrencies like Bitcoin are reasonably safe from an attack like this. However, newer, less mined crypocurrencies are much more likely susceptible to the 51% attack.
So my question is, how can new cryptocurrencies even form? It seems like people are forming their own cryptocurrencies left and right, even as jokes (see , e.g., dogecoin). How can new currencies get off the ground and gain enough critical mass to be reasonably safeguarded against a 51% attack? Why don't most new cryptocurrencies get killed off nearly immediately by an attack like this?