I don't see AWS doing this. They've continuously implemented technology improvements that have allowed them to reduce costs for customers 67 times in the last 10 years. The price of cloud services always goes down, not up, over time, as you're able to realize the benefits of improvements in compute power for the same cost (Moore's Law) without upgrading hardware.
Disclaimer: I work for AWS, but my opinions are my own.
If any of these companies is able to extract monopoly profits without fear of competition undercutting them or government/legal intervention, they will.
Right now all 3 are competing fiercely to win the hardware rental market, but this may not be the case in the future once the market matures, and they may raise prices to match leaving costs (as parent comment pointed out) if they can lock customers in.
The price must always go up over time. If there were a first rule of business, that would be that.
Price decrease is just a longer term strategy where it goes down before it goes up.
Hint: the cloud market has PLENTY of competition.