It shouldn't be, and didn't used to be (I'm 40 so I've been around software dev for a while).
This kind of behavior is unprofessional and an embarrassment for our industry if we just consider it our industry standard.
It doesn't take much effort to draft a form letter rejection (that is generic enough to avoid any potential for lawsuits, if that's their concern) and even less to send it out. With just a minor amount of work they could act like they were adult humans who treated other people like humans... why not do that?
Heck, I don't think I even mind telling people it didn't work out, so if you get in this kind of mess with Google, I'm happy to track down errant Google recruiters for you for them to officially turn you down, or happier still, get you that offer that is waiting in some stalled process.
Big companies can be challeging to interview for. So many moving parts that translate into an offer. pre-interview, interview, referrals, manager and exec review, headcount allocation, comp negotiation, etc. etc...
FWIW, I've never gone through an interview here where I felt like I should assume I will be hired.
And with one exception, every time I have not been given an offer, it has either been the silent treatment or they wait until the very last day of time that they said they would give an answer (usually a week).
My rule of thumb is give the recruiter 3 days to 1 week before trying to contact them again.