With each phase, the skills and IQ needed to move from a proverbial taxi driver to a programmer role increases while the income from that new set of skill decreases.
Example: Take a Taxi driver in the 1970's.
And even on a relatively smaller paycheck (adjusted into 2018 dollars), for example, a baseline IBM COBOL programmer could support his entire family on one paycheck, and still live well.
The charts below show the transitions from a baseline role to an analogous role or new role and what skills are required, what are amount are transferable skills while highlighting the gap and jump required.
For instance, an old time livery employee would be analogous to a parking lot attendant (mass market) or perhaps valet (higher end).
A buggy whip factory worker would make gas pedals / accelerators at first, and perhaps today, fuel injection systems.
The other aspect shown is the skills requirements, gap, jump and impact in moving from one role to another (whether it is analogous or new) such as the proverbial taxi driver becoming a software programmer.
In each transition case, one can see how many more skills are needed, how many transfer and how large or small is great both the gap and the jump.
As a side note, gap relates to the amount of skills missing, jump relates to the market weight or market difficulty of acquiring and possessing a particular skill or skill set.
At the same time, if taxi drivers (and there are certainly outliers, however, we are not talking about outliers for the very reason that they are outliers) could make the switch and jump now (when it is far easier and pays far better) why would they wait until the future when they are forced to do so, and when at that time, when they are forced to make the change, the switch and jump will only get harder and pay relatively less, all while they lose the earnings under the curve having not transitioned.
Even more of the same could be said about the 1970's taxi driver as it was very easy then (relative to today). Yet it didn't happen, it isn't happening and it will not happen. And the reason should be and is abundantly clear in the charts below.