Unix: Why it suggested to create users for some applications?

Is it some kind of encapsulation when by some tutorials I am suggested creating separate unix user.

E.g. in tomcat installation instructions it said:

1 - Create a Low Privilege User

Running Tomcat as root introduces the unnecessary risk that a compromised Tomcat instance could yield control over your entire server. Thus, creating a user with low privileges to run Tomcat should be standard practice when installing new instances.

Question:

1. Is it single reason? What about installation under my sudoer user, not root.
2. What about different installation managers like Linuxbrew, how do they solve this problem?

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