I wouldn't really say they're "made" to go 120 MPH+, they're certainly capable of it, but they're not "made" to do it. At least when I think of something as being "made" to do something, I think it's meant to do that every day it's used, like NASCAR cars are "made" to go 200 MPH+ every single day it's used. They're not fuel efficient, but they were designed to be able to do those kinds of speeds long term and be relatively easy to maintain while doing it -everything is simple to get in and out of on those cars. Engines come out easily vs my 2017 Mustang, their tolerances are specifically set for those punishing conditions, the transmissions are standards and made to tolerate those speeds, etc.

If you drive your regular old street car at 120 MPH+ every day, especially an automatic, you're going to wear it out quickly -the transmission, engine, pulleys, belts, water pump, radiator... weren't designed to run at that kind of RPM for a long time. They were designed to run best at the 55-65 MPH range. As odd as it sounds, engines are actually designed to go through so many tens of millions of revolutions in their lifetime before they start to leave their tolerance parameters due to wear. That's partly why Scotty advises against buying used V8 sports cars without checking them out, cuz high speeds and hair on fire acceleration wear the engine out of tolerances way faster than grandma driving her V8 Cadillac Sedan DeVille at 35 mph in town and accelerating at a snail's pace. 

They pretty much go that fast because they weren't speed limited from the factory. They don't limit them lower partly because people would throw a fit, and they're easy to remove with a tuner on most cars.

Mainly for marketing.  Why do some vehicles (like my 2004 Corvette) have a speedometer with top speed of nice round number of 200 mph, when it can “only” do 175 mph (certified by test driver)?  To make you think you can go that fast (when in fact the vehicle cannot, and keep in mind the average buyer doesn’t know much about cars and it’s potential) does something to a person’s psyche.  Similarly, if you look at some of these crossovers, they advertise them going to remote, rugged spots in the world when in fact those vehicles will not and cannot go there (they would need to be rescued if they went off-roading in some of those places) - but the thought that “hey, my vehicle can go remote places” adds to the appeal, and they sell tons of vehicles that way.

you need extra speed for passing and evading danger

Just because it could, doesn't mean it should. 

Many German cars go on the Autobahn where there are sections with no speed limits. There is a gentleman's agreement between German car makers that they will limit the speed to 155mph, which is a safe speed to travel over there because, unlike here in the US, they have lane discipline and actually know how to drive.

Many cars say a speed more than they can go. I had a Silverado that had 120 on the dash, but 98mph was all you got. As others have said, you take a normal street car and run it hard, you'll shorten the life. That's one reason you see so many engines blow during police chases. They simply are not made to hang at high speed for extended periods.

Now, if you really want to party, try building a car that will smash the speedometer needle past the top end and bury it off the charts. That's how you get the party started. Just make sure you use it on a track. I've run the Texas Mile many times and there is a surreal feeling watching the needle go past 160mph and just keep turning after the numbers have stopped all the way to the peg. Quite a thrill, and completely legal. {black}:cool: