The problem with staying on your existing contract is if you have the entertainment package then it does expire, so you are then paying extra for it and can’t renew it without upgrading. Same with discounts, they usually have an end date so at some point you will be paying more. When you do upgrade, you find Vodafone have introduced a new top tier plan and has started removing benefits from lower plans like global roaming plus and EU roaming, so you will have to pay more for the same benefits. It’s all about increasing revenue.
EE has also started forcing customers out of the minimum term onto new contracts, so do nothing and you still get forced onto a CPI+ contract without EU roaming. History shows that when EE do something, Vodafone soon follow, but not in a collusion type way of course.