It's a deliberate expression of power.
It's exactly like Putin forcing his cabinet to publicly support his war, one by one.
His useful idiots can't complain about Musk after this. Trump publicly demonstrates that all power flows from him, personally.
Trump is implementing, piece by piece, the exact same playbook Putin used to turn Russia from a nominal democracy into an autocratic dictatorship.
The following has already happened.
The legislature in obeisance. The media controlled by friendly oligarchs. Opponents in physical fear for their safety (withdrawal of security). Public demonstrations of power over friendly politicians. Corruption of governance with oligarchy. Military leadership purged of independence. Independence oversight of voting systems compromised.
Watch the courts get nobbled next. Direct violence against opponents follows, and then US is what Russia currently is.