It's easy to talk about training people.
I spent a lot of time training people in my previous job only for them to come back to me with basic questions about what I taught them over a year later.
What was missing was technical leadership from above: the managers didn't realize (or value) the need for the team to get familiar with the systems that they were working on, so they didn't make sure that the team learned these things well, or brought in a few more people who could guide them in addition to just me.
In many places there is always something urgent and there will never be a good time to slow down. Then you end up in my first point eventually. So part of your job is to create that breathing room, push back on projects, get people trained, etc. Think long term and not just moment to moment.
edit: And if you think training people now is painful, doing so when you're actually past the breaking point will be be a lot harder and cause a lot more disruption.