Small group for 50 people

Generally, joining groups is actually a smart move since it greatly improves your odds of winning gibs. However, there are generally two types of groups that gt featured here:

Promo giveaway group:

These groups are usually public and are made to promote something. Be it a person, games, etc., their goal is to get as many members as possible. The reason is to give more visibly to what the are promoting in the first place, but it also allows them to have something to offer to devs who more often than not provide the keys for these giveaways. Making giveaways can be extremely expensive, so to offset the cost, these groups approach devs with these large member base and offer their games exposure if they sponsor these giveaways. While this works well for the groups and devs, this usually means the members "lose out" since they are competing against a large bas for these games. (Though I should stress that your odds will be better in these groups than in public gibs).

Ratio based group:

These groups have low memberships due to the strict requirements that re needed to enter. They usually involving having a certain ratio, meeting group admins in group chat, making some type of app, and even then it is not guaranteed that you will be accepted. If you do managed to get an invite, you are usually required to make a gib first and do not enter any till yours has ended. This works as a pseudo-probationare period where they can make sure you are not tring to take advantage of the group. Once past that point, you are expected to maintain a certain ratio (vary among groups) which is in place to prevent peeps from entering/winning everything but contributing very little. Many view these groups as "randomized trading" which is sort of right in a way but not completely true.

The problem with the op and so many other peeps like him is that he has not established himself as a user on this site. The lack of giveaways that he has made, and the fact that he is attempting to limit the user base of his group (while not being picky about those who are entering) leads on to suspect that he is attempting to artificially increase his chances of winning. By inviting a bunch peeps and encouraging them to make gibs leads on to suspect that he is attempting to take advantage of others generosity while limiting his contributions as much as possible.

In the end of the day, you should join groups where you (the member) are benefitting from the situation. If there is any hint that someone might be taking advantage of you in anyway, you should bail. The owners/admins/mods of groups should be pulling all the weight to keep it running and not give the impression that it's members are expected to do the work for them.