That's basically the design of the entire Suica system and similar systems, such as Octopus in Hong Kong. Octopus has been in service for over 25 years now (which means it was probably designed 30 years ago), with Suica at over 20 years. One of the primary design considerations was that mobile readers be able to validate and deduct value from the cards without connection to a central server. Consider the use cases of buses and taxis, and that mobile data wasn't a thing back then like it is today. Like a lot of things, you'd design things differently today than you would 30 years ago. Also prior to what's happened with the Internet, the notion of service providers wanting to individually track everything to monetize the personal data of their customers wasn't a thing. Even with today's technology, I see a lot of benefits of the decentralized design of these systems, which include the ability for casual purchase of cards for cash without having to sign up or register.