Ok so many clans have been saying that you need to be forum active in order to have a higher chance of making it. Why is this so? Also how does one improve forum activity that the recruiters looks at? Thanks in advance <3

Being forum active means you post alot, which tells people you're not going to be inactive or feeling like quitting the clan any time soon.

Right

and most clans are forum based(like they are on the forums a lot), so they want people who has great amount of activity inforums (and ingame if needed).

it's easier to interact and get to know people through the forums, so if you're forum active enough they can get to know what kind of person you are, rather than if you're just good of bad at the game

You'll find that the clans that don't require that tend to not last for the most part. Clan threads/boards are ways to actually contribute to your clan while being organized. Figuring out times to get together and play, setting up events hosted by your clan, talking to any members you might not have caught in-game, etc. are all things that can't happen in-game. Don't forget a good clan thread is being active and productive with the space used on here, and helps your chances to becoming an official clan.

Improving your forum activity is as simple as you can make it: Post more. Look around the forums, post replays you might have enjoyed, share them with video editors who ask for them, look at the art your community creates, get into marketing, and so on.

Clans usually want to create a small community. This is hard without communication. The forums offer a centralized method for communication. Therefore forum activity helps your chances of being accepted to many clans ^^.

As to what they look at, initially it'll be your post count . You improve this (obviously) by posting more. Be careful though, posting just for the sake of post count can lead to you be infracted for spamming or posting useless replies. Also, some threads only add to your post count once, such as some Clan threads, so posting many times in these will not improve your post count.

However: in the first place, you should not be posting for the sake of post count, but because you actually have something worthwhile to add to a thread.

Good luck :P

Most clans are forums based, thats why they want forum active players who contantly posts in the clan thread.
Also, if all the members of a clan is forum active and posts like once per day in their clan thead, there is a big chance of that clan to be official or something.

The clans want you to feel engaged with them, not just be a clan hopping ass so just post stuff whenever