Okami had touch screen support, RE5 and 6 are the only versions of those games with gyro. Those sold the most (along with REvelations, which happened to be the first Capcom ports on the system).
Conversely, RE4 underperformed, even relative to RE5 and RE6 (!), and DMC1 and 2 presumably did too, leading to 3 getting more effort put into it.
Why spend more money when previous products may have tanked? Because Capcom recognizes the potential for higher sales with their catalog products on Switch (reinforced by higher effort ports actually having done well), and so is trying to appeal to a potentially lucrative market with a bit more investment.
Literally basic economics.
Its not basic economics that if the first two DMC ports did awfully to go all out on the third. The assumption would be Switch owners don't like DMC not Switch owners only like enhanced ports (if adding in something as basic as gyro / touchscreen equates to enhanced). You are going against what the market is telling you. Basic economics would be to cut your losses and not release anything.
Also what numbers are you using? Okami sure did not sell as much as RE4