What a proper decking job involves
Decking is load-bearing right where people stand, so the work that matters is underneath. On a rebuild the old boards come up completely so the joists can be checked and treated, or replaced where they have softened, before anything new goes down.
New boards are laid with a consistent gap for drainage and movement, and the edges get a proper finishing trim instead of butting straight up against the patio or the wall. It takes longer than a quick patch, and it is why the result lasts.