During those times, multiple church modes were reduced, hindering the freedom of modulation. Eventually, more “major” and “minor” keys became available and Bach took the chance of opening doors by utilizing all keys theoretically available. His collection is deemed to be very significant historically as it launched new avenues for future generations.
Although whole collection was published 51 years after his death, that didn't stop the world from recognizing Bach's unique artistry and musical contribution. There came the modern editions of the collection and also over 150 recordings of this celebrated collection documented until now, with transcriptions for synthesizers and ensembles.
Learn more about it at: https://galaxymusicnotes.com/pages/learn-the-background-of-the-well-tempered-clavier-by-j-s-bach