the Secret Service has an annual budget of almost $2.5 billion (though they do have some responsibilities aside from protecting POTUS)
In much the same way that the USMC has some functions besides providing West Wing sentries.
"Hey Sheryl, where are we gonna hide our offensive computer security team's budget?" "Let's put them dozen as 'personal security' for Mark."
And they get to use more exciting/expensive tools that would otherwise be illegal for private citizens/companies to use.
They spend the money because it's not their money, because they can, and to flex on other leaders who are more budget conscious. Even for Zucks a billion a year on security theater would be a bit rich - because he spends his own money.
[0]https://www.sccgov.org/sites/da/newsroom/newsreleases/Pages/...
[1]https://sanfrancisco.cbslocal.com/2021/08/17/update-embattle...
https://www.secretservice.gov/about/history
We are one of America’s oldest federal law enforcement agencies, originally created in 1865 to stamp out rampant counterfeiting in order to stabilize America's young financial system. By the end of the Civil War, nearly one-third of all currency in circulation was counterfeit. As a result, the country’s financial stability was in jeopardy. To address this concern, the Secret Service was established in 1865 as a bureau in the Treasury Department to suppress widespread counterfeiting.