There are a lot of ways to interpret this question, as shown in by the variety of responses in this thread.
But we could rephrase it to "why aren't top speeds limited to the maximum speed limit?".
It's got me thinking about the creeping culture of safetyism, especially against the current backdrop of Covid-related restrictions.
In some ways it makes no sense that cars are not restricted to a sensible top speed. Either a simple dumb limiter set to the top speed limit for the country, or something more sophisticated using GPS (or a combination of the two). Doing so would possibly (probably?) save many lives per year. Yet it's unlikely to happen because:
1. there's a powerful automotive industry that relies on cars retaining their power as a status symbol
2. there are a lot of powerful and influential people who enjoy driving fast cars.
It frightens me that we are seemingly only able to retain our freedoms when there is some powerful industrial lobby to protect them.
People are currently being subjected to much, much greater restrictions of freedom than having the top speed of their car capped. Entire livelihoods are being destroyed on the basis of "saving lives". Perhaps this is justified. I personally don't think so but a convincing argument can be made.
If there's a conclusion to this, it's that we need to move past the "if it saves some lives, it's worth it" style of argument.
It sounds brutal, but some values are worth holding on to even if they kill people. You may balk at that statement, but you implicitly accept that compromise every day, even if you've never explicitly thought about it.