Correlation does not equal causation. There's a very broad spectrum of people who do not have degrees. It's very likely that if you took those same people earning degrees and had them enter the workforce instead, they'd have equal or greater pay.
To put it another way, earnings are correlated with an individual's talent and drive. Currently, many of those people end up getting degrees. It's a correlation, it's not the degrees that are causing the jump in earnings, it's the individual's skills.
To address your separate point directly, there are studies that attempt to directly answer the question you’re asking. For example: http://conference.iza.org/conference_files/CoNoCoSk2011/gens...
However, your conclusion isn’t shared by the authors. They show a positive return on college degrees, it’s just smaller than the unadjusted difference in income.
One probable factor for this is cultural bias toward giving jobs to people with degrees, and paying employees more who have degrees. Individual skills alone do not explain the difference in earnings, so despite the fact that talent correllates with income, the correlation is not 1, and thus it is not likely that the same people earn equal or greater without a degree than with. It is likely that the same person without a degree will earn less than with a degree, on average.
In fact, the labor productivity growth rate does not seem to have significantly changed at all, even as the percentage which is college educated has gone up a lot: https://stats.oecd.org/Index.aspx?DataSetCode=PDYGTH
To address your point directly, I don’t personally believe that non-grad programmers are as economically productive as grads on average. I would totally believe that non-grads are as productive at building UI widgets and CRUD apps and stuff like that. However, inventions and patents are absolutely dominated by people with postgraduate degrees. It’s not a matter of hourly output, it’s a matter of yearly compound interest, and the compound interest in computer programming is generated by research. It is overwhelmingly PhDs who are developing neural networks and AI methods right now, overwhelmingly postgraduates who are the architects of new hardware and of new software methods. These are the things making the computer industry grow larger in fundamental ways.