He's got 99 problems and well...

Most likely this is a category of 401k (or IRA) called a SEP IRA. It works to the company's tax advantage and they have the ability to force it on all employees. All employees is a requirement of this. I don't have a ton of knowledge about this, but about a decade ago I dug in to it because my wife's company did this to us at a time we really needed more flexibility on what she was contributing. I don't remember the nuances, but sadly I found it out that (at least at the time) while it seems sketchy as hell, it was legal if the company met all the requirements/followed all the rules to do this.

I think it's less that "developers think this is okay", and more that this was an alpha stage project prior to the Reddit meltdown and influx a couple of months ago, and they've been working their asses off to keep the site up and stable, and are working to evolve the functionality to meet the need as soon as practical/possible.