I think the fame/infamy that lasts thousands of years may have more to do with impact on the world rather than heroics.... or whose stories were told at times where access to written stories were limited. It may genuinely not be possible for anyone nowadays, despite being truly heroic, to be remembered for such a long time because it might not be possible to have such a huge impact on such a large percentage of the population.
I'm not even sure if we need legends now, thousands or millions of small acts of kindness within local communities is probably more important.
I don't know... it's definitely an interesting thought exercise.
limited story telling (in writing at least) is a big part of it. There were many stories never recorded.