I've worked for some years in restaurants. Guess what everybody hates? Having their work interrupted by phone calls.
Would you like to have your work interrupted all the time by phone calls?
Today I consult for restaurants and help them get their web presence and the reservation systems they need on their websites. They are very happy for this.
A restaurant usually has their booking calendar open on a display that all the chefs and waiters can check when they walk by. The system doesn't need any human to "apply" reservations or cancellations.
And there is a big difference between being interrupted to take bookings, or checking bookings when you have down-time. But thank you for your hacker sarcasm.
Guests usually call during the day to book tables for the evening or for another evening. In the afternoon between lunch and dinner, there is more time for staff to check bookings. Instead of answering the phone in the middle of morning prep or lunch service.
Then there's events. A venue can have public events with hundreds or thousands of participants. Usually during high season. So now you'd have that additional burden of phone calls, which becomes completely impossible unless you hire additional staff to only take calls. Or you have your own online system which is available 24/7 for customers to make and even pay for their bookings.
Third party reservation systems take anything from 15%-25% to do it for you, which is not really great for the restaurant, compared to buying their own system.
Or if it's an online system for take-away orders or deliveries, these get sent directly to the kitchen ticket printer.
And it's the same for the other small business category: accommodation. The best thing they can do is have their own online booking systems. To increase sales, reduce burden on staff, and reduce expenses to third party providers. And give customers a better experience.