I do not think there is a requirement to get the reload or other bonuses like weekly/monthly bonus. I'm quite sure I wagered less than $1,000 in the last 30 days before the July's monthly bonus but I got the bonus. Afaik all existing account get the offer, but it does not mean that Stake is throwing away free money since the amount is just so small and not all those inactive accounts claim the reload. It is also part of marketing to make those inactive accounts come back by giving them few satoshi/cent from the reload.
It is not a big deal to throw away some dust money, but it has a positive marketing effect. You can get nice bonuses like weekly/monthly bonuses only if you are a regular user who wagered frequently. In general, other users' bonus allocations are limited; I generally receive between 2 and 3 cents. The rewards depend on the performance of the user. I think it's a great marketing strategy.So yeah, I do believe that dusts get together and build something huge, not something like millions but definitely thousands of dollars combined and that is for just nothing, just as a "thank you" for the ones who gambled, that is a good thing.
I have no proof of this.... but it does not make any difference in the fairness of the "draw" of these giveaways. 
stake.com's birthday is August 7-8th, right? In anticipation you have to make $1000 wager and at least place a $1 bet on sports , this is a requirement i always see in every telegram drop. 
