It's not just profitability but also management. There are other reasons including:

• if we lower too much, it's opening door to abusers who create multiple accounts. We manually upvote for quality control so this would also create too much work.
• if someone delegates 1 SP, they should receive 10 SP upvotes which is virtually impossible to do with our current Steem Power. It's not even 1% vote weight... 25 SP is the minimum we can do.