The benefit is that the president is not subject to retaliatory lawsuits (similar to what the Trump administration is now doing against e.g. James Comey, et al), the threat of which might prevent them from performing their duties effectively while in office.

I’m sympathetic to your concerns, agree that it was a poor ruling, and frankly think we need a constitutional amendment to address the excessive power the presidency has, but the justices aren’t making these rulings without having a real, justifiable rationale behind them and they aren’t making these rulings because they’re in the tank for Donald Trump (Justice Alito excepted)