Why did Nokia, Motorola and Ericsson decline?

The selling point of mobile phones in the era of functional machines is shape design. In the era of smart phones, the selling point is who has more third-party software, more configurations and more appearances. Ericsson was the first to decline, then Nokia, and then Motorola, but only their terminal products, that is, the mobile phone you mentioned, in fact, people still have patents to make money with other communication equipment, but they don't use mobile phones as terminal products.