If you think you can set up mail infrastructure with on premise everything that is available to your not on premise workers safer than Microsoft, you will be spending a huge amount of money to do so.
It just turns out that the US has become a rogue state that alligns with the type of war criminals and dictators that the ICC wants to prosecute. I really don't think anyone would have predicted this 10 to 15 years ago when this mail choice was made.
Which is why I specifically phrased the part you didn't quote in that specific way.