Also, the first try of drawing boundaries will always be varying degrees of wrong. If you have very strong boundaries at this stage, iterating on them, moving responsibilities around, can be harder.
Also, with the right tooling it's definitely possible to harden monolith internal boundaries to a comparable level.
I can see though how many smaller companies would not be in a position to build that tooling.
Anyway... there is no either / or here, as I've explained in another comment. What if you have components within a monolith, but each component has its own database, for example? What if test suites are completely isolated, so that tests for component A can not access code in component B?
You can get pretty strong boundaries with a few comparably simple tricks.
This in turn has a positive effect in maintaining proper boundary and putting the right amount of thought about the interfaces and responssability of each component.