We know why. The game had to ship on a date, and those responsible were not willing to delay the launch date on the basis of performance issues.
You would think a little more time would be put into reaching at least some reasonable performance level.
Unfortunately, negative publicity from bad performance doesn't really stop these games from selling well, as proven by most AAA releases in the past few years.
The studio already killed a series once with a bad second entry, cities in motion 2...
Oh yeah, everyone remember the Panama papers? Yeah seems the public have forgotten about them a long time ago. What was done about em? Humans only remember some things.