You make a good point. However, consider that there are big players on Steemit who already have a large stake in terms of audience and steem power. Your idea would make them 10x richer. Small fish like you and me would never stand a chance of getting our voices heard because we are competing with people with endless portfolios of content. At least with the 7 day limit, the big players have to keep producing content instead of kicking their legs on the table and watching their bag increase in value.