Not everyone is using Exchange Online.
But you are probably a much less appealing target. Also, you might be willing to lock it down more than Microsoft, which has to please all those millions of customers and wants to admin it at the lowest cost possible - including possibly minimizing support calls by using permissive settings - and not with the most security possible.
If all your staff are in a country, there's no reason for your internal tools to be accessible from any other country. If all of your customers are in a country, there's no reason for any of your web presence to be accessible from any other country.
these days it looks like every email is a teams message anyways, so unless they also release onpremise teams server, i don't see a future of exchange very bright
maybe everyone will move to google workspace in the future?
2019 is technically still receiving feature updates because of the delay of the new Exchange on-prem, though however that transition takes place will be wild.
And what if the unbundling doesn't affect the price? Don't confuse MSFT making mediocre products with them being commercially stupid.