Because it's in all these countries interest to avoid a race-to-the-bottom and being played against each other by companies that only need to move a mailbox to change jurisdictions.
For examples of the same mechanism: Amazon's HQ2 farce aptly shows what happens when jurisdictions cannot effectively coordinate and are forced undercut each other. Is there any doubt that Amazon would settle in some city and hire people and pay taxes without their little version of Hunger Games? So the net effect is simply some city being marginally better of but forgoing the jackpot that would usually come with being chosen, and therefore those citizens having to pay instead.
Plus the harm that comes from Amazon making decisions based on money alone, to the detriment of other factors such as quality-of-life for its employees.
That's why any trade deal includes provisions prohibiting subsidies not covered by a few narrow exemptions: they distort the competition and simply lead to losses in a zero-sum game between nations and private corporations.
For examples of the same mechanism: Amazon's HQ2 farce aptly shows what happens when jurisdictions cannot effectively coordinate and are forced undercut each other. Is there any doubt that Amazon would settle in some city and hire people and pay taxes without their little version of Hunger Games? So the net effect is simply some city being marginally better of but forgoing the jackpot that would usually come with being chosen, and therefore those citizens having to pay instead. Plus the harm that comes from Amazon making decisions based on money alone, to the detriment of other factors such as quality-of-life for its employees.
That's why any trade deal includes provisions prohibiting subsidies not covered by a few narrow exemptions: they distort the competition and simply lead to losses in a zero-sum game between nations and private corporations.