Did NVIDIA's ascent to a 1T company result primarily from their substantial software investments, or is there another element that AMD needs to focus on to achieve similar recognition and adoption in the realm of GPU compute?

It's mostly software. Nobody gives a damn about your AI chip even if it is better than what AMD has and AMD's hardware is no slouch.

The other factor is that AMD's data center hardware is not available at any cloud provider so nobody even has access to the supposedly supported hardware.

NVIDIA let you run CUDA on consumer GPUs and AMD didn’t let you run RoCm on consumer GPUs. Big mistake