A more simple analogy: it's an insurance.
It's certainly wise to subscribe an insurance for your house, but for every single drinking glass you own...?
If it's a tea set you inherited from your great-grand-mother, when you break it the insurance won't un-break it. If your property suddenly needs to be more than a property, chances are that this change will break the LSP or trigger a larger redesign anyway.
A helpful (to me) metaphor is that you're paying for an option. (In the finance sense, not the type system sense.) Sometimes it's worth buying an option, sometimes it's not, but don't think it's free.