Apple's assumption (which is probably backed up by usage studies) seems to be that "real professional users" use their laptops portably,
and use lots of weird ports, but almost never
at the same time. So the laptop itself can be lighter to encourage that portability, while the ports can live on a dock at a desk (e.g. the Cinema Display, an older iMac, or that multi-port USB-C dongle that will probably just hang permanently off all the cables it's been joined to.)
For those exceptions to the "almost" never—mostly IT people doing field support—they make a litany of adapters. Adapters make sense for this use-case: the target type of user already carries many in a "toolbox", and this is just adding on a few more.
And don't forget the Mac Pro. Apple's own internal "real professional users" are, as far as I know, more likely to use a Mac Pro at their desks and then a MacBook for mobile portability—but they won't bother to try to do work with the MacBook that'd be better done on the Mac Pro. Which includes plugging strange peripherals into it.