I have about 120 paying restaurant customers, and I couldn't agree more about the PDF menu. You could give them the slickest, easiest interface in the world, and they'll never use it. They don't have time. The PDF menu already looks good, they already put a ton of time into it to get it exactly right, and they don't want to duplicate that effort. Restaurant menus are meticulously laid out and a lot of effort is put into their creation. It would take a lot more time, and a whole lot more money than 95% of restauranteurs would be willing to put into it to create HTML menus. It would be very difficult to generate a menu creation tool that would please even a small percentage of restaurant owners, since they all want wildly different things, and are almost universally very picky about their menu.
There is exactly one reason why most restaurants have bad websites, and that is money. The average price they're willing to pay for a website is $500-1800. It's rare to hear of one paying over $2,500. It's not necessarily that they're cheap, it's that they have no money, or think they don't need it at all, so only want the bare minimum. The good restaurants don't need a website, they have a two hour wait every time it isn't raining, and the restaurants that do need a good website have no money.
Most people grossly overestimate the profitability and ease of running a restaurant. I estimate that as many as 40% of restaurants are run unprofitably in perpetuity because the economics of the location are impossible. The owner purchases the restaurant, runs it for two or three years, runs out of money, sells it to the new owner who runs it unprofitably for two or three years, runs out of money, and the cycle repeats. You probably sit in restaurants like this regularly and think, "This place must be a goldmine, it's always packed." It isn't, it's a money pit and the next guy that buys it is going to discover that as well. If you are thinking of starting a restaurant to make money, I suggest you purchase the land and build a building that can house a restaurant, then lease the space to someone else, it's the only reliable way.
Running a restaurant is also a lot more difficult than most people think, and many owners amplify the difficulty by having little or no business management experience or training. They got into it thinking it would be easy, and thought they could handle it because they've been eating in restaurants forever. Take order, cook food, serve food, simple stuff, right? Restaurant employees are always stealing from the restaurant, especially the bartenders. Customers can be very, very difficult. The staff will be flaky. There will be problems, constantly and forever. It's not easy.