I think the Bloomberg link is a classic Scare Story, and I doubt that almost 2 in 5 remote workers are working two full-time jobs.
That said, if they were -- and their employment agreement doesn't forbid it -- what's the problem?
The claim that they're getting sub-par results is an a-priori assertion without any proof. Further, companies themselves have migrated towards at-will employment, in which it can be terminated at any time for any reason, as well as migrating to defined contribution pensions and increasing employee contributions to health care, transforming the work relationship into a series of transactions in an effort to maximize profitability. It would be foolish to assume that the other side of the equation wouldn't eventually mirror the practice.
I also hear a lot about "work time," which is another interesting concept in 2022. When does it start? When does it end? Do workers get to drop off calls immediately once "work time" is over? If they have to work longer hours than those with "work time," do they receive extra compensation? It seems to me that the expectations around "work time" suddenly disappear when additional time is required... which means that it's not really a reasonable basis for making determinations from.
Some employers seem to "want it all," and the world has changed.
Employers who treat their people well will retain them and attract new people. Those who don't trust their employees or micromanage them will have difficulty attracting top talent. And people at successful companies will, as always, be evaluated by output, rather than presenteeism.