For a long period of time the Azure Functions team focused on Azure Functions Runtime 1.0, although there was a version 2.0 publicly in preview. Runtime 2.0 had a lot of breaking changes compared to 1.0 and this was ok, since it was a major version change.
Many have tried version 2.0 and ran into a lot of problems, because version 2.0, now based on .NET core, was incompatible with fair amount of SDK libraries.
Since then the Team changed a ton in Runtime 2.0! Not only is it now Generally Available, they also changed the hole runtime model. Workers run out of process, workers can run within a Docker-Container, binding-extensions can be created and brought in by developers.
This is just a glimpse on the changes and the improvements of Runtime 2.0.