They do that because that’s the only way they can survive against AMD given how much behind Intel is in terms of CPU and GPU tech.
I have a really slim laptop featuring an AMD APU (Ryzen 7 7735U with Radeon 680M) and nearly 8 hours of battery life (browsing and office stuff), and which I can use to game (mid settings in games like Genshin Impact, on a Wayland desktop thanks to high quality open-source Linux drivers) and do GPGPU programming exactly as if I was writing CUDA thanks to their open-source HIP SDK (again, on a slim as fuck laptop with just an APU, AMD is surprisingly catching up very quickly in the GPGPU programming space this year, a few months ago I wasn’t able to get HIP code to run).
Neither Intel nor NVIDIA offer anything similar right now (Intel’s OneAPI DPC++ doesn’t count as “exactly as if I was writing CUDA”).