Interesting post. I haven't thought about it in exactly those terms, but something similar, and lately I haven't taken part in many giveaways either. One reason is that if I comment I give an upvote - more so that I can quickly see if I have entered than because I think the giveaway should earn a dollar for ever 5 cents worth of prizes - and that takes away from the upvotes I can give to other posts. And sometimes I'm so tired that typing "I'm in !LOLZ" on yet another Rising Star post just doesn't seem worth the effort when I can easily earn as many starbits by playing the game instead.
Splinterlands giveaways though, for me who can't afford the spellbook (at my current estimates of how many decades it would take me to earn its value back by playing,) each card I can win is a plus. And someday in the future, perhaps, I may have won enough cards that buying the spellbook would make sense! So that way, even small prizes are good. And what do I know? Maybe the person who does the tiny, daily giveaway really needs the profit to buy food or send their kids to school?
As for contests requiring some effort - post a recipe, a story, your thoughts about a topic - I think they are great fun, and often want to join, but the deadline comes and goes while I'm still thinking about my entry, and after a few days I have 20 tabs of expired contests to close 😹
When it comes to big curation accounts automatically upvoting the giveaways, I know too little about how that works to really have an opinion about how to solve it. It does sound bad though - if I delegated my HP or followed a curation trail, I would want my votes to go to "real" posts.