Microsoft cannot promise developer incentives that actually scale. They have run several "hackathons" and "app contests" and things with eye-popping prize money, like $100k and whatnot.
But for most people, supporting an additional platform for any duration more than a year can quickly cost upwards of that amount. With the tiny marketshare today, and nothing but hope that it will ever grow - hope that has not come to fruition in 3-5 years - it will be a net loss very quickly and also have diverted resources from the other aspects of the developer's companies.
If they could perhaps offer scalable incentives, like "support and consulting services worth $2000 per month" or "we pay you $0.05 per download (even if your app is free)" or "we'll market your app alongside WP marketing" then perhaps. Perhaps it might be functional developer incentive.
Disclaimer/note: As a cofounder of a company built around an app that Microsoft tried to woo us to port. We toyed with their APIs for a bit, but it was going to be a support nightmare with our hardware and sensor requests and we decided against following through.
They had to block native code on WP7.x because they were on the CE kernel, knew they were going to move to the NT kernel in WP8, and native apps wouldn't have ported over.
Platform agnosticism is something that Qt exists to provide... Your point is taken that the Qt backend would need to be ported twice. For WP8+, I suppose that would involve a DX11 port of ANGLE for Qt5. Which seems to have been merged in, actually https://codereview.qt-project.org/#/c/52810/. What was WP7? DX9? Angle covers that, as well. So, I'm not sure why we're not seeing it, at least on WP8+ given that it does have native code support. https://msdn.microsoft.com/en-us/library/windows/apps/jj6816...
But for most people, supporting an additional platform for any duration more than a year can quickly cost upwards of that amount. With the tiny marketshare today, and nothing but hope that it will ever grow - hope that has not come to fruition in 3-5 years - it will be a net loss very quickly and also have diverted resources from the other aspects of the developer's companies.
If they could perhaps offer scalable incentives, like "support and consulting services worth $2000 per month" or "we pay you $0.05 per download (even if your app is free)" or "we'll market your app alongside WP marketing" then perhaps. Perhaps it might be functional developer incentive.
Disclaimer/note: As a cofounder of a company built around an app that Microsoft tried to woo us to port. We toyed with their APIs for a bit, but it was going to be a support nightmare with our hardware and sensor requests and we decided against following through.