Its because a small group is in control of 90% of the power, they and their "community" that have been given some steempower deligations because they think the same way are all upvoting what their small group likes and flagging stuff they dont. the main page shows what the biggest people on the site think is "quallity" for "muh community".
What can be done about it IDK, but that is the reason for the main page looking like it looks.

The system may be decentralized but the power distrbutition isn not. And thats not even going into premining the system to get your power.

EDIT:
voting services and alt accounts sure dont help. just more consolidation of power to the powerful for a couple bucks