Why people herd themselves towards closed ecosystems
The main reason is that open ecosystems cost money to run and in turn charge their customers. I pay actual money for my IMAP email service. Closed ecosystems can give their services away in exchange for monetising their users - but only because the closed system prevents the users from leaving.
The other problem with open ecosystems is that they can be buggy and unreliable. IMAP was a real mess for much of its early life and finding compatible combinations of client and server implementations was not easy. Much easier to provide a reliable service if you control it end to end.
Of course, open systems are more likely to persist (sometimes well past their sell-by date: IPv4, SMTP...), but a lot of these closed ecosystems are short-term fads so their longevity isn't an issue.
This may not be desirable in terms of the overall good of mankind, but it's unanswerable in the marketplace.