I would think the sense of seamless integration contributes to the experience. Almost all third party software systems have integrations and plugins that make crossing over between Google suite and these near painless.
Obviously this would be solved if we had a way to centralize our identity and file storage and such across platforms and systems. Yet at the moment the silo is what makes it seems painless and increases its value beyond the fact there’s a substitute to each platform and product.
Integration, management, accessibility, auditing and compliance for starters.
Tech folks love to say "X is is perfect substitute for Y" in the same way they say "what's so hard about X, I could write that in a week" by considering only simple ideal workflows.
The real value, and the real moat for these products, is that they're tied in with SSO and other products, easy for organizations small to huge to manage, have dozens or hundreds of specialized features crucial to large organizations. They comply with legal regulations, accessibility standards (which ARE legal regulations in many jurisdictions such as if you want to sell to the government), and more.
Writing an email server is perhaps 2% of the work involved in building an email product.
Obviously this would be solved if we had a way to centralize our identity and file storage and such across platforms and systems. Yet at the moment the silo is what makes it seems painless and increases its value beyond the fact there’s a substitute to each platform and product.