The only way they diminish is if someone finds a better solution. So far no one has. It is only near a monopoly because the others are so much weaker.
If the EU gets their way and make Google cough up their “mysterious algorithm” for “monopoly’s” sake, then all bets are off. There was a story that the Chicoms were able to hack and steal that algorithm because one employee at Google left his pc on at Google HQ and they were able to extract it..