It's the best data that's available at the time. It's been collected in a consistent fashion for a significant duration of time. To understand how a new methodology would differ, we'd want to run a new process in parallel for a couple years.
A few notes from an interview on the Odd Lots podcast, interviewing Bill Beach, former head of the BLS:
* Response rates among surveyed employees are roughly:
Month 1 68%
Month 2 83%
Month 3 93-94%
* Large employers tend to respond sooner, and are staffed to handle these requests better.