Lawyers have both continuing education and pro bono work expectations, both of which are frequently also bar membership requirements (with some common
exemptions, IIRC, for the pro bono requirement in jurisdictions where it generally applies.)
Of course, because they are binding requirements and because lawyers as a norm (and, when not working as regular employees of their direct client, usually a legal requirement) work for other lawyers, this is usually accommodated within working arrangements. But software developers don't have industrial guilds or self-regulation, so they don't have the same kind of power to get accommodation for the need for doing things outside of their current narrow job duties accommodated within most working arrangements. But that doesn't lessen the need for it.
> Doctors about the diagnoses they make for fun on Saturdays?
Doctors are much like lawyers, including both the binding nature of continuing professional education requirements and, and least broadly, the reasons why it gets accommodated in their working arrangements.
> Teachers about their open source lesson plans?
No, but, teachers also have mandatory continuing education requirements as licensing conditions outside of what they are immediately teaching. And they tend to have strong unions and legal requirements to point to to get these accommodated in their working arrangements.
Software developers have, as a whole, implicitly opted for immediate pay over other advantageous working conditions, including accommodations for continuing education, but it is no less relevant to their ability to develop and perform. Possibly moreso than the other fields; tooling and practices in software development evolving more rapidly than many other intellectual professions.
It's a little harder to pin down than side projects, but the activity is still there.