Doesn't anyone who spends a decent amount of time on the internet these days have a lot of contact with mediocre writing?
Yes. I question the merit of that advice too. "Read a lot, the best books possible" as a strategy will still result in reading far more mediocre writing than optimal.
You know how bad the worst released stuff is? That's still the good stuff - the bottom of the barrel is at least in the barrel. The slush pile has horrors. Worst is the stuff that's just ... not good. Being able to identify why helps you learn from others.
Granted, writing is not very effective. But some of us just love writing...
Earning to Give Writing: Which are the places that pay 1USD or more dollars per word?
Mind Changing Writing: What books need being written that can actually help people effectively change the world?
Clarification Writing: What needs being written because it is only through writing that these ideas will emerge in the first place?
Writing About Efficacy: Maybe nothing else needs to be written on this.
What should we be writing about if we have already been, for very long, training the craft? What has not yet been written, what is the new thing?
The world surely won't save itself through writing, but it surely won't write itself either.