Where I work, the difference is basically, making things that already bring in revenue continue to work = maintenance. It is about the decay over time, but also

Where I work, the difference is basically, making things that already bring in revenue continue to work = maintenance. It is about the decay over time, but also the cost of just making business, keeping the lights on. Just as you need to pay your cloud bills to keep your service running, you need to have a certain amount of developer-hours addressing things that do not work perfectly and needs adjustments and fixing. For the developer in question it may not matter much, it is git branches and continuous deployments just the same, but the distinction is not really for the benefit of the developer. It is for the manager that can reason about different opportunity costs by knowing how much time and money maintenance work needs.