Agreed that the economics sometimes does not make sense. However, if you wait until your current movement takes a dump and you replace it with a new movement, there's no guarantee as to how old that 'new' movement will actually be. It could be a 5 - 8 year old movement sitting in some watchmaker's bin to begin with. Oils age and dissipate over time regardless of whether the watch is running or not.
For a Seiko movement, that mentality may be well and fine. However, there were folks who had the same standpoint when it came to ETAs. Since they were easily sourced and affordable a few years ago, the same mindset was in place to just replace instead of service. Now, with the cost of Swiss ETAs as it is, it's a different perspective