"Seems to work" is not the same thing as "Working As Intended". I work on Gmail/Inbox (previously GWT). When we released Inbox, it started out as Chrome only, people discovered they could get it to load and seemingly work on Firefox by spoofing, but the reality was, it was still broken, and would eventually consume all memory, because Inbox relies on sparse Javascript array behavior for protobufs, and something like…
For many years Firefox was the largest browser that wasn't IE, yet no such launch happened.
Even when Chrome's marketshare was below 5%, Google always launched Chrome-only.
Your argument is nice, but ultimately invalid: Google never cared about providing to the most users first, but only about giving an advantage to their own spyware browser.