Why is it raising a budget instead of a bid?

When a campaign runs out of budget it stops serving for the rest of the day, usually in the evening when conversion is strongest. If it is doing that while under its ACOS target, the constraint is the budget, not the bid.

Raising bids on a budget-capped campaign makes things worse — the same money is spent faster and the campaign caps out earlier in the day.

The raise is gated on efficiency, verified Stock cover, and your account daily cap. It will not chase a runaway.