There's some weird history there. For most of the project's existence, Scala 3 was known as Dotty. It was basically a research project, and it was recognized from the beginning that it was a different language than Scala, largely due to the type system semantics...the goal being a formally defined, fully sound type system (Scala had some edge cases that made it not sound, even if it was more sound than most languages).
However, the language resembled Scala, was created by the same person, had some cool capabilities that a lot of Scala users longed for, and it was a chance to "start over" with some of the more questionable design decisions that had been made previously, so there was a lot of questions and pressure to make it Scala 3.
So it was decided to no longer treat Dotty as a second language, but rather to find a path to migrate the existing Scala ecosystem to this new language. This transitioned the project from a relatively slow-paced research language into a full fledged and funded project with an urge for engineering not just tool and ecosystem compatibility, but also bytecode compatibility with Scala.
So for most of those 8 years, there was no objective but to create a better language than Scala. Then very rapidly (maybe the last two years), it went from "this is a completely new language" to "these language ideas will be incorporated into Scala 3", to "this will actually become Scala 3 and we're working on a transition path".
And from the perspective of someone who was aware of Dotty and a regular user of Scala, that felt like an extremely fast transition. Especially for a language that took years to make much smaller changes in the past (2.10->2.11->2.12 felt like an eternity).