"...there's a problem with there not being any reason to hold SP except to earn curation rewards."

The problem is stake-weighting VP, because it allows the extraction of the majority of the rewards, and prevents that value from inuring to the Steem price by creating more demand, as it would if it was reaching the content creators. The media payout is .01 SBD, and the average payout is ~15 times that, revealing that a couple dozen whales are extracting more than an order of magnitude more than the entire rest of the community.

Wanna grow the price of Steem? Grow the market, not the wallets of whales. ROI from extracting the funds from the marketing division of Steem directly discourages ROI from capital gains, and that's the problem that has not been addressed by any HF. HF21 halves author rewards, doubles curation rewards, and gives the whales another tool to increase their ROI too: the downvote pool. Every time whales flag rewards back into the pool, they get another run at it and extract ~90% of it.

Until stake-weighted VP is no longer is able to extract the rewards that create interest in Steem in new users that grow the market for Steem, capital gains will remain elusive. Profiteers are not investors. They are a plague.