I agree.
Freelancing/contracting/consulting is statistically the only way to part time work in professional fields.
One reason is that the basis of a freelance/contracting/consulting relationship is that the freelancer/contractor/consultant is solving the company's problems. But the reason people seek part time professional work is focused on solving their own problems.
I mean it's great that the OP wants to set up their life for writing. But it's hard to expect a software company with no personal relationship with the author to absorb the overhead for that dream...
...the people to ask to support the writer's dream are the writer's readers.
Working as a consultant/etc. means the author absorbs the overhead for their day job. Those costs can be built into the rate.
And of course, 80-100 hours of billable work as a freelance software developer usually entails an equal amounts of billable and unbillable work.
Rates are higher than direct salaries to make consulting/etc. viable.