Not sure why this is downvoted, it's a fair question in the US. Tipping culture is gross, and this is coming from someone who was a bar manager for a bit.
But to answer said question...
- You make a good recommendation, you get a good tip, that simple. Helping your table explore the menu + what they're into translates to happy customers and better $$$ for you later
- A lot of the high end items are loss leaders[1], part of the decoy effect[2], or are there just to round out the menu, e.g. how a seafood joint will have a steak or burger option for the spouse or kid or kosher person who doesn't do seafood.
- Front of house staff get told to push things depending on what's in stock or what is in season. Like, we have another shipment of meat arriving on Monday, so let's sell off as many braised spare ribs as possible to make space. A lot of our daily or weekly specials were based on what had to be tossed out in a week.
[1] https://en.wikipedia.org/wiki/Loss_leader
[2] https://en.wikipedia.org/wiki/Decoy_effect