Yes this has nothing to do with the customer. This has to do with the waiters, hostesses etc who know how to use the system and to get them to us another system would take time to learn.
But the article says it is "shitty" and that "most hate it". I think it might be due to:
[1] There are issues in all software (bugs, lacking your pet feature, etc), and people like to complain.
[2] The article's author has developed a product in the same space (although it seems to be more of a restaurant website template, rather than a reservation system), so there might be some jealousy there.