Rpcs really can't be understated in terms of the effect they had on classes and inheritance.

While in theory it should be straightforward to ship instance state over a wire, in practice most languages have no built-in support for it (or the support is extremely poor in the general case; I remember my first experiments with trying to ship raw Java objects over the wire using the standard library tools back in the early 2000s, and boy was that incredibly inefficient). Additionally, the ability to attach arbitrary methods to instances in some languages really complicates the story, and I think fundamentally people are coming around to the idea that the wire itself is something you have to be able to inspect and debug so being able to understand the structure in transit on the wire is extremely important.

Classes and their inheritance rules make exactly the wrong things implicit for this use case.