Google said this was mostly because developers had worked out ways to game the system. It said that compiler optimisations needed to achieve high benchmark scores have become common. However, in the real world, these optimisations translate into only very small improvements in webpage performance.
In fact, in other instances, it was found that tactics used to boost Octane benchmark performance had a detrimental effect on real-world performance. Developers exploited known bugs in Octane to achieve higher scores than were warranted, and Google believes the time has now come to retire the system completely.
The move is not unexpected as Google has been moaning about what developers have been doing for a while and had been running down the benchmark for ages.