Internal training can lead to degregation and failure

If you source systems from outside sources but for cost-saving reasons purely rely on internal knowledge hand-over to get joiners up to speed, it may lead to degregation of the process.
Take a rapidly expanding company but strictly cost controlled like Ryanair. Many of their core systems are sourced from 3'rd parties but maintained in-house. However what worked yesterday and today might not be as effective tomorrow. Most companies throw more manpower at a problem. This is specially the case if non-technology people are set to solve system problems. And the users of the system may know no better because this is the way they do the process and that is the way their predecessors did it.
However the developers of the system might have come up with new solutions and ad-ons because other companies using the system also have experienced similar problems. And since these other companies have invested in from-the-source training, the resulting near contact have led them to ask if the processes can be automated better. These improvements cannot be picked up through internal training unless all system documentation are made easily and publicly available and somebody sees an interest in, and reward for, being up to date on all new developments. And many system developers keep new stufff close to their chest, as a competitive advantage.
Problem is many companies only reward new processes that leads to direct monetary rewards. Not for keeping going old-reliables that have always worked but are core to the successfull operation of the business.