Is the fact that almost no startups talk about or use Oracle that much of a problem for Oracle? Those startups wouldn't have generated much revenue for Oracle anyway. Those startups will forever be in search for a free solution.
Oracle doesn't go after startups. Or even companies like Facebook or Dropbox etc.
It goes after: government agencies, banks, insurance companies, multi-nationals, huge retail chains, logistics, payroll, and such. And it does a killing at it.
Web style big-data are not Oracle's domain.
And it's not like those startup people will afterwards (when they "grow up") go work in the enterprise and use Mongo and MariaDB there. It's just different kind of problem domains altogether.
As per my comment above, Oracle doesn't care about those startups, whether they become the "software giants of tomorrow" or not.
They sell to government agencies, logistics, payroll, multi-nationals, banks, finance, insurance companies, etc.
Those sectors do not overlap with the startups using MariaDB, Mongo, or what have you. Totally different problem domains and people.
* Last I checked, Oracle allowed you to use Oracle RDBMS free for "prototype development" but once you were actually generating revenue from that you are supposed to buy the necessary licenses, even for continued development or support purposes.
Hm... I vaguely remember (but it was a really, really long time ago) you could use Oracle for as long as you wanted as long as you didn't process your own or your customers' business data.