The Alliance for Open Media has launched it's first video codec in early 2018 and it gained lot's of traction ever since. Alongside the ever developing software encoders which are built by AOM members there were also changes in the internet noticeable for everyone:
But most importantly, AV1, contrary to HEVC, is free and open-source. It's royality-free nature enables every provider and every device to support the codec without paying AOMedia a cent. This is key to get wide ranging support and drive adoption.
In contrary HEVC requires expensive licensing royalities to use as a company and it's IPs are a mess.