I can't argue for the original person, but when 500 large projects are different instantiations of just a handful of fundamental primitives, it is not hard to keep track of large number of projects which might look like completely different non overlapping projects for an outside observer.

With enough competence, it boils down to an exercise in organizing discipline and first principles derivation. As I have mentioned in the past, skillsets at sufficient granularity are transferable across domains.

What you said would be true when looked at each different project as a separate domain, but real world is rarely a collection of isolated domains.

To put that in perspective, our app SlypBusiness has memberships, products, services, gift cards, privilege cards, etc. which all look like different domains to a user but is fundamentally the same primitive instantiated differently.