Says who? Personal experience on the carrier side, dealing with tens of thousands of people sticking their 8 year old SIM into iPhone 12/13 and wondering why they can't get 5G. Less calls into customer care or trips to the store getting a new SIM = "benefit to carriers".
Says the hundreds of carriers and MVNOs globally who don't have plans to transition to eSIM and can't offer services. Compared to the corner case of grandparents sticking in 8 year old SIM cards?
There's definitely zero benefit to carriers. It's pretty obvious which group is the "many" and which is the "few."