It's the principle of 'Defence in Depth'. Do both, as one control may fail.

Security is done in layers. Yes, we do our best to keep the adversaries outside the proverbial hatch. But even inside the hatch, the principal of least privilege is important in reducing the damage of attacks.

Typically you do things like this to either work in restricted envs (distroless) or to evade detection logic. It's not about bypassing a boundary, it's about getting things done in the env you have available.