Not speaking specifically for the OP, but for myself, having a quiet, controlled place to wait while one parent is getting lunch, etc. is a requirement. I have two children w/ neuro disabilities, including autism. Trying to get them to stay in one place w/o moving and w/o having a meltdown from the overstimulation of people bumping into them while hungry is a physical impossibility. We are also limited in where we can sit, to avoid a child eloping, we need to sit with them against a wall. That is for their safety and the safety of others- primarily to prevent one of my kids running under the feet of someone not looking because they're carrying a tray or two. So if there isn't a suitable table, we don't eat there. Also, we need a table where the kids can be somewhat contained because there's only one of us watching them. We keep some snacks and distractions with us at all times, and work very hard to keep them engaged.
For all of the reasons stated, the "solution" you propose is completely unworkable. and fwiw, we do eat at off peak times of day and during value season so the crowds are as low as possible. Sometimes it is very difficult to have empathy for someone who has a different disability and therefore different needs. Hopefully this is a place where we can educate and support each other.