I don't think it's brand loyalty on the part of end customers, it's just unlikely and difficult for a number of large vendors to coordinate on such a project. You would need motherboard, CPU and GPU designers to take a long bet on a new form factor, while also cutting their bottom line (SoCs require less components and better performance for money)

I think the speed advantage would be one welcomed by the average PC user, and if Intel aren't already colluding to make an answer to M1, they're heading towards extinction