How about common courtesy? Its not all about me. Its about not inconveniencing others just to make it easier for me.
Think about it. If there are 100 tables in a place and it takes 15 minutes to eat, then the restaurant should be able to handle 400 tables in an hour. But if people now occupy a table for 30 minutes at a time because they are reserving a table, then you've cut the restaurant seating capacity in half.
Like it or not, reserving tables works against you.
I don't see this as "table holding." I see it as multi-tasking.
Once a family of 4 finds a table, they will take 10 minutes or so to get the kids into chairs and/or high chairs, get napkins and condiments, and get ready to eat, then they will take 30 minutes to eat. Total table time - 40 minutes.
Or, part of the family can get in line during that first 10 minutes, then bring the food, and everybody eats for 30 minutes. Total table time - 40 minutes.
Not much difference, unless the line for the food is really long. Of course, the line is shorter if families put an adult and all the kids at a table instead of in the line...
I travel solo. I have no kids or wife to "hold" a table for me - I have to take my chances when I get out of line, like everybody else. But I would rather see families sit at a table and let one or two people get in line than see cranky kids forced to stand in those narrow queues, clogging them up and preventing others from placing their orders.
It's just common courtesy to everyone - both the families and the solos - to clear out the lines and let them move faster, and to let the kids relax instead of standing in a line that they don't need to be in.
So I say, hold those tables, folks. I for one won't give you any crap for it.