Especially in "tech," job tenures are generally shorter than they used to be. It wasn't at all unusual at the big computer companies of the 80s and 90s to have a fairly large group of employees who had worked at a company for a decade or two (or more).

For various reasons, on both the employer and employee side, this has changed a lot especially when you're talking startups--but also companies like Amazon from what I understand. In any case, if the expected tenure of an employee is only a couple of years, it's probably unreasonable in most cases to have a 6-12 month training period during which the employee isn't especially productive.