Hive SBI was originally set at 1 HIVE (or 1 STEEM in a previous iteration) at a time when that was roughly $4. The intent was to encourage people that have to provide more support to those that have not. (Crowd-sourced so it stacks support from lots of different people into a single chunky vote).

Hive blockchain has a minimum payout threshold of $0.02 (any posts with payout total below that are dusted and receive nothing). Since many Hive SBI members are newer Hivers that don't regularly receive a lot of votes, the SBI vote is sometimes the only sizeable vote. As such, we have set a minimum upvote threshold of $0.02 so that our votes are never dusted. (Pending vote value accumulates for each member until an $0.02 upvote can be delivered).

Supporting a 1/10 size HSBI would make it more affordable, but it would make it take even longer between upvotes for 1/10 size members. It would also mess with the new member economics (new members always start with $0.06 so they can get their first upvote immediately) and significantly increase the amount of abuse in our program. At present the level of abuse is very small (largely because the long payback period that you mentioned in your post is NOT attractive to abusive accounts - they want to cash out quickly before they get caught).

We encourage new Hivers that can't afford full units to get involved in our Discord server. People regularly post contests and giveaways that make it easy to build up an initial stack of Hive SBI.

We will also be relaunching the Hive SBI Writer program soon. That is also a good way to accelerate your Hive SBI membership level.