Because they do. The police aren't going to race after you at 200+ mph. They're going to follow much slower and catch up to you once your effective speed falls to 0 mph.
The function for drag force increase over a speed increase is dy = dx^3. That means if you double your speed, drag force increases by a factor of 8. So doubling your horsepower doesn't double your speed. Even if you assume the doubled horsepower is transmitted with no losses to the wheels and converted perfectly to forward motion (it isn't), a 2x increase in force translates to, at best, a 25% increase in speed.
Then there's controlability. I'm sure you could make a 300 mph car (in fact the current land speed record is Mach 1.02, albeit using jet engines), but it would be uncontrollable on anything other than a perfectly flat, perfectly straight, perfectly cleared road. For example, the land speed record holder had to be run on a cleared, graded lakebed.
When racing, what matters most is handling. Second is acceleration. As long as your top speed is 150 mph+, top speed simply doesn't factor unless you're drag racing or are on a static track like Nascar. Top speed doesn't matter because there are very few situations in actual street racing where your speed will exceed 150 mph regardless of what your car's design top speed is. You'll crash before you get that fast. The only places I've ever driven faster than 150 mph are on long, flat freeway straightaways.
You want to go fast and not get tickets? Get a radar detector, a laser detection system, and a laser jamming system (the last one might be illegal where you live, but you can still install it since they're fairly low profile). Get an app for your phone where people mark speed trap locations (there are several). Set all that up in your car, and slow down when any of those devices indicates the police are ahead. It may be difficult to suck it up and admit it, but the police have you bested in this situation.
Hell, they don't even have to catch you. As long as they get your license number (or if you have a relatively uncommon car and they notice the make, model, and color), they'll show up at your house with a ticket, or with a warrant for your arrest if there's something else they want you for.
They can still get your car's make, model, and color, and if it's an uncommon/sporty car, they'll have a lead to who you are. If they care enough, they'll start with finding hard evidence of you doing shit and give you a ticket or arrest you.
Congratulations dumbass, you just bought yourself 1+ year in the Nigger Pen! Cops have a computer to look up DL numbers and find out who owns them. What will they do when they look your fake ID up and nothing comes up, or someone comes up who is the wrong gender/wrong age/looks completely different? What will they do when the person with the DL number you gave them lives on the other side of the country and none of the vehicles registered in their name is the same or even remotely similar to the one you're driving?
Here's what they'll do: they'll arrest you for carrying a fake license. And while a speeding offense is an infraction (not even a misdemeanor, meaning you get a $500 fine tops, no jail time, and a hit on your driving record), falsifying identification can be a felony, meaning you're in the land of mandatory minimum jail time. It also means you're never going to get a job that doesn't involve flipping burgers. And you better hope they don't find evidence that you were trying to take someone's private information to get a semi-believable fake ID, because if you do that you've graduated to full-fledged identity theft, which is another felony.