Not a diabetic but adult later onset lactose intolerant and the problem is you really have NO idea what restaurants put into stuff, even if you ask.

Even a stupid salad, what's in the dressing, what's in the bread/croutons, what was the meat glazed with. Etc.

Restaurant food tastes good because it is generally unhealthy top to bottom, with quantities of salt, butter, etc no sane person would use at home.

One thought experiment - when was the last time you ate out and needed to add salt to anything? Now thing of home cooking how often you might add a little salt while you are eating.

The easiest thing to do is ruling out restaurants entirely, but then that's rather anti-social.. Not to mention family/friends gatherings, etc.