I don’t know who gives that advice. But from personal experience I’d say it’s like this in most companies. Everyone has a job to do and tasks to finish. Nobody has extended down-time to train ‘the new guy’. Especially the experienced people you’d like to learn from have important stuff to do.
Some employers like their workers to actively solve their problems. So you could try to be more proactive and vocal about it. Say you’re not familiar with that project or tech and you need a more detailed explanation. Tell them what you didn’t understand and ask where you can look it up.