This is a dumb response. First, they don’t build the car to attain a specific speed - in fact they actually limit the car’s maximum speed afterward.
Second, they don’t design and build the car just for the US. There are plenty of markets with higher highway speed limits (or no limits). Third, there are places in the US where it’s legal to drive faster than 85mph (including, of course, race tracks).
Restricted access highways and empty straightaways in the middle of the country are different from city and rural roads with cross traffic, traffic lights, and stop signs. Treating them differently and having stricter limits for the latter is very sensible. Especially as they wade into uncharted waters.