In my country, as you can't just switch customer's plans at will, the telcos structured them as limited-time offers that have no commitment or penalties on top

In my country, as you can't just switch customer's plans at will, the telcos structured them as limited-time offers that have no commitment or penalties on top of a regulated base pricing which is like 2-4x the going rate. After a year the offer ends and you can keep your current plan at the expensive base rate or you can move to a new plan/offer to get the discounted market rate. That way they can justify increasing rates over inflation and changing contracts at will.