Those markets have a much stronger network effect (especially social media), or were/are propped up by aggressive antitrust violations, or both.
To use your example, the problem with entering the phone market is that customers expect to buy one phone and then use it for everything. So then it needs to support everything out of the gate in order to get the first satisfied customer, meanwhile there are millions of third party apps.
Enterprise GPUs aren't like that. If one GPU supports 100% of code and another one supports 10% of code, but you're a research group where that 10% includes the thing you're doing (or you're in a position to port your own code), you can switch 100% of your GPUs. If you're a cloud provider buying a thousand GPUs to run the full gamut of applications, you can switch what proportion of your GPUs that run supported applications, instead of needing 100% coverage to switch a single one. Then lots of competing GPUs get made and fund the competition and soon put the competition's GPUs into the used market where they become obtainium and people start porting even more applications to them etc.
It also allows the competition to capture the head of the distribution first and go after the long tail after. There might be a million small projects that are tied to CUDA, but if you get the most popular models running on competing hardware, by volume that's most of the market. And once they're shipping in volume the small projects start to add support on their own.
To use your example, the problem with entering the phone market is that customers expect to buy one phone and then use it for everything. So then it needs to support everything out of the gate in order to get the first satisfied customer, meanwhile there are millions of third party apps.
Enterprise GPUs aren't like that. If one GPU supports 100% of code and another one supports 10% of code, but you're a research group where that 10% includes the thing you're doing (or you're in a position to port your own code), you can switch 100% of your GPUs. If you're a cloud provider buying a thousand GPUs to run the full gamut of applications, you can switch what proportion of your GPUs that run supported applications, instead of needing 100% coverage to switch a single one. Then lots of competing GPUs get made and fund the competition and soon put the competition's GPUs into the used market where they become obtainium and people start porting even more applications to them etc.
It also allows the competition to capture the head of the distribution first and go after the long tail after. There might be a million small projects that are tied to CUDA, but if you get the most popular models running on competing hardware, by volume that's most of the market. And once they're shipping in volume the small projects start to add support on their own.