I think they should give people what they want - a high powered upgradable machine. If they don't want to make it upgradable, then they should at least refresh it annually.
Having content producers using macOS is a huge benefit to their brand and I think it's a big part of driving sales of their iOS devices. At the very least, if they lose the content producer market there will be significantly more friction to producing iOS apps.
Yes, there's a halo effect, but I don't think it's all that huge especially with respect to video pros and I bet it mostly works in the other direction - people like their iPhone so they are more likely to buy a macOS laptop or desktop. Nobody is buying a Mac Pro because they like their iPhone.
The driver for iOS development is profit and as long as iOS users are willing to pay more for apps, it will continue to dominate. And if you want to make an iOS app, you are going to buy a Mac, but probably not a Mac Pro.
The Mac Pro is like the iPod in that it exists in this weird space where it continues to be sold but is clearly not something that Apple thinks is important.