I can totally understand your point, and SBI-shares is a wonderful gift! I will give each user SBI shares too because I truly believe that it will encourage people to put in even more effort. Effort often equals rewards, so it's important to encourage and educate.
That being said, the concerns you brought up are valid, people tend to leave Steemit once, A) They don't earn as much as they expected or B) When the rewards decrease. Either due to support or the actual value of Steem.
Unfortunately, it's the sad reality we have on Steem. But, by empowering others, we will not only strengthen the middle class on STEEM, we will also encourage these users at the same time. I know the feeling I got when I recieved a delegation for instance. I was eager to put in more effort than ever before. It was a way to show my appreciation and to give something back.
So, along the way to minnowhood, these users will put in more effort, engage more and also, get more support outside of Minnow-ASAP so to speak. They will build their profiles and grow their personal followings. With all of that, comes also increased rewards. And, ultimately, they will most likely want to give back to the community, so I see it as a win/win-situation.
My main reason for donating Steem/Steem Power directly to users are to give them a "jump-start" in terms of motivation and encouragement. Besides all of these things, there are things like the Redfish Power UP League and/or the Curation and Engagement Leagues. I obviously recommend those to everyone, but especially these users, as it would yield them even better results.
Who, why, how and when people decide to support is entirely up to them. I don't judge anyone based on how they support or what they believe is the best. I will focus on doing things my way, having my own reasons. If others do the exact same thing or not doesn't matter, as long as we, at the end of the day, are trying to strengthen the middle class. :)
Cheers for the mention of the leagues, we got this one for the Minnows too:
https://steemit.com/community/@steemcommunity/the-minnow-power-up-league-week-26
50 STEEM each week going out as liquid or @steemmonsters cards, courtesy of @yabapmatt. 30 + bounty + SBI's from the EL, and 6 SBI's from Paula for the Redfish. Plenty to help as long as folks are aware.
Good luck with #minnow-asap!