Why did St Vincent stay at Toulon instead of pursuing Napoleon?

Why did St Vincent stay at Toulon instead of pursuing Napoleon himself and leaving a junior officer in charge of the blockade?

The larger French naval force remained at Toulon, and its escape could threaten Gibraltar or other destinations. St Vincent kept responsibility for that danger and sent Nelson after the expedition.

The larger French naval force remains inside Toulon after the expedition leaves. Its escape could threaten Gibraltar or allow operations elsewhere, so containing it remains the senior commander's responsibility. Napoleon also lacks the importance he will acquire later, which changes the apparent stakes of a personal pursuit. St Vincent can maintain the blockade while sending Nelson, his aggressive deputy, after the detached force.