What's the purpose of putting a level on giveaways?

As I understand that you have limited familiarity with the topic yourself, I assure you that when you put the concept of making public giveaways into actual practice, you'll find that results are just as negative as forum hearsay suggests. My public giveaways have been overwhelmingly negative, and low level public giveaways have been nearly nothing but- even in the few situations where rule-breaking and auto-joining and bot use and multi-accounting wasn't absolutely certain, many of the remaining winners ended up admitting or even bragging about such things regardless. The sole reason I didn't leave the site early on was due to the ability to do group giveaways and later, due to SGTools being introduced. Likewise, the sole reason I continued doing occasional public giveaways was due to the ability to add level restrictions to such giveaways (to minimize risk of issues occuring).

The only money I ever got throughout my life was from birthday gifts, and Christmas gifts.

Many of us don't even get that. While your perspective on the site isn't exactly wrong, your accusations of paranoia and your seeming outlook of "well, I may give back one day but I don't really want to, even though it's really cheap and easy to give away a few bundle games" don't color that perspective in a very positive way.

Hopefully, once you have a job and learn to appreciate the demands involved with obtaining and managing money, you'll be able to present a more appreciative consideration toward the site. That is to say, the site doesn't exist to give things to those who can't get such themselves. It exists because people are willing to give things away to those who can't get such things themselves. The nuance may seem slight but, in actuality, it's a fairly major distinction.