quick question

You don't.

We don't need to, but

a) Some people like to express their thanks and do so

b) Some people don't want to have a bad comment-to-entry ratio and have a bot/script set to comment 'thanks' on every giveaway they enter

It doesn't have any impacts, but if the GA Maker asks a hypothetical question, he or she may enjoy reading the answers.

thanks
Some creators blacklist people who just write generic "thanks" because they assume they're bots

Also be aware that some people will blacklist you for commenting and some will blacklist you for not commenting, and some will do it if they just don't like your comment. As a general rule of thumb, read if they have made any specific demands in their descriptions and otherwise stick to commenting if and only if you win.

no wonder i got blacklist form others in my stats ._. never did any wrong though. lol

I usually never comment on entries unless I have something to say. But I always comment if I win.

well beyond the "thank you" and possible gifter requests, the comment section is also the best place to discuss any issues with GAs. such as: duplicate key, region-locked keys, wrong title GA, please re-roll i already won/own, etc.

what about comments makes a giveaway look fake though? that part doesn't make much sense to me.

I avoid commenting when entering cause i dislike the spam .

Some ppl do it cause of respect ...

There is solid portion who use autojoin scripts leaving comments like that .

Tbh i find it unnecessary to post Thanks , unless you won ofc .

You don't need comments anywhere, there are many people who only use this place to get free stuff, and never say a word...

But if you want to thank someone for buying a game for a complete stranger, instead of keeping it for themselves, I'm sure it wouldn't hurt anything. :) And if someone asks a question in the giveaway description, maybe they would like to hear your answer... Or maybe they are just checking who's a human and who is using a giveaway-entering script... :)

If someone writes the identical generic thanks in every giveaway they enter, I think that looks insincere, or at least lazy. :) If you're trying to win a game, but you can't think of a single thing to say about it, maybe you're trying to win the wrong game... :) Oh well... :)

I love comments, even if they written by bots.

When you have 30 GAs running and bots stick 20 auto-"thanks" in each one, your inbox is blown up with 600 messages. It's really annoying, so I can see why people blacklist those spammers.

Personally I only thank a few giveaways manually, usually AAA and personal wishlist giveaways, with a few random ones inbetween.
From the viewpoint of a giveaway creator I don't think thank comments are necessary. I don't mind them and won't blacklist anybody, but I just don't care whether or not people comment.

This question has already been answered here: https://www.steamgifts.com/discussion/p5RCd/why-do-we-need-to-give-a-thanks-in-the-comments-on-every-post-giveaway-we-entered

sometimes it's better to be fake than look ungrateful.