Now, you must also have a functioning system, and so you may take risks by leaving things more open than you would like if you don't have the resources to thoroughly lock everything down.
But wherever locking things down further costs you very little, you should take the opportunity. And elsewhere you should asses what level of protection you can afford. Ultimately it is a cost-benefit analysis. Many risks are not worth spending money protecting against. Others are vital.
But even disregarding malicious users: Individual user accounts is not just a protection against malicious users, but against careless users. When someone sets a password that gets guessed, you want to be in a position where exploiting that persons credentials is as hard as possible, and tracking down actions taken via the account is as easy as possible.
And yes, you could insert something into a build script. But if the build script is committed, and the commit was pushed from a named, individual account, you're now at the risk of going to jail. Creating deterrents is often a sufficient risk mitigation strategy to be acceptable.