The problem is that LTS proponents pretend that those costs disappear when in reality you are actually paying them as a huge sum every once in a while and that sum is usually much, much higher thanks to something comparable to interest (also compare to the technical debt analogy) than the actual small costs of frequent change.

That is partially because you are adopting the changes at the wrong time (e.g. if everyone introduced a new network protocol version 3 years ago and you are only doing so now you have 3 years worth of problems the new version solves and interoperability issues with the part of the world that introduced it all roughly at the same time to each other), partially because adopting huge numbers of changes obscures the reasons things break for you when you do introduce changes and partially because change is not routine so you forgot lots of things since the last change and have to rediscover them.