Canada

In both the Western countries I've lived so far (France and Italy, but my guess is the list is much longer), this wouldn't be possible.

The landlord could at most adjust the rent to inflation.

The only wag he/she could ask for such a steep increase is by making a brand new contract with someone else, but for that purpose the current contract should be terminated, which isn't possible if your occupants are paying their rent, unless he/she wants to re-take possession for selling the apartment/house or to live in it. If they fake the repossession and actually end up renting again to an inflated price, the new contract is deemed void and the previous occupants could be reinstated.

It makes any other sort of renter protections moot if they can basically be evicted whenever by saying the rent is now $1,000,000 take it or leave it.

No one should answer you seriously, because that the most braindead question I've read.

Because people need housing to live in, so it's in the interest of the vast majority of people to make sure the few that own property can't increase rent by 100s of % for no good reason. Additionally we live in a democracy so usually the interests of the majority are supposed to guide policy making even if it upsets the minority that control access to resources because they won't profit quite as much as otherwise.

Found a landlord