Mainly to increase their Voting Power, Resource Credits, and hopefully for the ROI to become better in the future.

The way I see it, HIVE is really an undervalued platform, so chances it skyrocketing in value one day aren't impossible. If more people believed this, the won't be slim either.

Also, having more Hive Power when you're using the platform daily feels good, regardless of it being a good investment or not.