Agreed. Does anyone have any insight as to why companies fail to do this? Naively as a non-{marketing,business development,COO} guy, I feel like the cost to keep delivering those services ought to pale in comparison to the value of having even a tiny number of those customers go into a forum like HN or Reddit and say "we've been there since the early days and we're really happy".
Sure, it's inherently a tech/financial/support load to maintain a special category of customer, but I don't see it as fundamentally any different from a successful company managing the discontinuation of a popular product. You cut off new customers, let attrition take its course for the existing ones, and take your lumps from any high-value/high-touch customers who drag their feet on moving to the new thing. It's work, but so is climbing a ladder. Do you want to elevate the company or not?