They have no choice but to raise prices when 1/2 or more of their tables are empty and they have costs over what they had before. The restaurant business is not very profitable so they don’t have fat they can cut. What would you prefer? Raise prices which will stay raised. Add a surcharge which they will drop when things are back to normal.
If a restaurant can raise prices and still fill its tables available, so be it.
It's a matter of supply and demand, pure and simple. If the market will bear the addition cost of eating out...great. If not, tough.
It's a tough business.