Losing out on the best deal. Coupon codes on checkout and other such places

I’m used to seeing coupon codes online, but don’t see it so often in stores. where online can take the lead from bricks and mortars stores.
(c)  Ambernectar 13

Image © ambernectar

In physical stores they will only display discounts and coupons that everyone can claim. e.g. 20% off everything in store.
whereas online there is quite frequently the “enter code here if you have a coupon”

I saw for the first time, a restaurant that offered 20% off your meal if you presented a cinema or a theatre ticket.
I was literally entering the restaurant when I saw this advertised on an a-board outside.
seeing this and knowing I had neither put me off immediately. I didn’t want to pay full price whilst others were getting it cheaper. it sent me on a five minute hunt to find the nearest cinema. and when I realised I wasn’t going to get a cinema ticket. we purposefully chose another restaurant to eat at.

Before seeing the sign I was on their doorstep ready to go in, but bailed at the last second.

I wonder how much addition business they gain by running this promotion compared to business lost through people like me being put off? To my mind it’s a case of the offline world copying the online, where offline had the right approach in the first place.