A (Potential) Bird in the Bush vs. One in the Hand?

There's that old adage: A bird in the hand is worth two in the bush.

As I understand it, it means a sure thing (even a small sure thing) is better than a potential big payoff.  

But some recent experiences suggest that certain Chicago restaurants may not be adhering to this adage - and their service may be suffering as a result.

Take a recent experience I had at one of my favorite restaurants. A reservation at another place had fallen through, I was a few doors away from this place and stopped in to try to get some dinner. 

I walked in the door to the warm, bustling dining room. I noticed that about 2/3 of the seats were empty. I humbly asked the hostess "Do you have room for an unreserved diner?" She looked me up and down, surveyed the room, and said (somewhat snippily) "You'll have to sit at the bar." Hungry and wanting food, we headed for the bar. 

As soon as I sat down, i opened up OpenTable on my phone.  The restaurant in question had reservations available every 15 minutes all night.   I had a (lovely) dinner at the bar, and the restaurant never got more than 1/3 full.

This has become a regular problem for me recently.  I'll check my phone, see that a restaurant has tons of availability and then walk in and be told it's a two or three hour wait for a table. I could walk outside, make the reservation, walk back in and be seated immediately, but as a walk-up, i'm out of luck.

I'm sure there must be a business rationale for this, but damned if I can see it. Isn't a bird in the hand (a customer ready to spend money) better than a potential reservation that will never come? Is this the curse of instant online reservations? Or is it just a case of a bad run of snobby hosts who think that walk-ins are dirty bums?

In any case, it's not great customer service - and anyone with a smart phone who checks a reservation app is gonna feel like they are being duped.