I think it comes down to business mechanics. I think it’s often the case that Apple-ecosystem customers are more willing to pay for a product, allowing the company to have a direct relationship with stakeholders. It’s quite nice to charge a customer money, respond to their questions and feedback, grow together, succeed together. Advertising and other non-paying solutions do not have such powerful interest alignment, particularly for smaller and more artisanal brands. So business are choosing customers that support this more harmonious alignment by going platform-specific.
(In my case, I simply don’t have enough resources to support Windows, Android, and web versions. For Minimal, Windows is the most requested second platform.)