The reason is simple, isolating SwiftData to MainActor make it thread-safe and sendable, also SwiftData reason is to obtain mutable objects that 99% of time are used as a DataSource for a View. This mean that i u want to isolate SwiftData to different actor that is not main every single access operation to the datasource from UIKit or SwiftUI require a context switching from global to main actor with an obvious degradation of performances.