In a personal project that makes a lot of sense (and in a personal project you have your choice), but once you are in a corporate or open source project of more than just a couple of people, code is read far more often than it is written, and by many more people than the original author.
In those circumstances, it makes sense to optimize for readability to everyone rather than the author’s personal preferences. One can easily argue that Google’s style isn’t optimal, but it’s harder to argue that a personal preferences free for all is optimal.
The fact is that the limit of 80 characters length is arbitrary. No evidence that code of 80 characters length is more readable than code of 83 characters length.
The other fact is that few devs craft their code to fit 80 characters. Instead they write code and let formatters do their thing. But automated formaters are doing a horrible job, aka if I write a line that is 81 characters long, they will massacre it to a set of unreadable lines with no proper aligning.
So now we are at the mercy of automated formatters that try to enforce an arbitrary constraint that is irrelevant with today's code editing/reviewing technologies.
In those circumstances, it makes sense to optimize for readability to everyone rather than the author’s personal preferences. One can easily argue that Google’s style isn’t optimal, but it’s harder to argue that a personal preferences free for all is optimal.