If my six person startup has issues squeezing as much value out of my Dev than FANG companies with all their support structure and research into this, this is only to be expected, imo.
So yeah, it's a problem, one on the list of many problems most companies have though, so it's oversimplified to simply say:"Let's just pay for expensive training and hope they stay."
Yes, you can foster a culture, build a sense of loyalty etc. but at some point in time even the most loyal employee feels underpaid if he's paid below market because the company can't afford someone at the stage they've reached by working there. I've seen this play out too often to ignore the counter argument.
The incentives of the company and the worker often simply don't align when it comes to career growth.