Confused about planet progressions

[Millenia]

So Ive been wanting to defend the deep mantle forge planet for a few days now.
But for some reason every single day the planet is below 1%
why?

[Mandemon]

What planet are you referring to? Claorell, place where the Deep Mantle Forge is located, is under Super Earth control and is not under an attack. So you can't defend it, naturally. In fact, no planets are under attack right now.

if you mean liberation (AKA taking planets back from enemies of democracy), you can't do it alone. Each planet has "health points" and regen rate, and that regen rate is (almost) always greater than anything a single squad can do. That is why proper liberation requires multiple people invading the same planet to overcome that regen rate.

You can use Helldivers Companion to check regen rates for various planets. You can use that to make up strategies, but in general best way is to follow Major Orders and what is affectionately called "The Blob".

The Blob is basically largest concentration of the players.

[Vespertellino]

There's probably not enough players on it to progress, as enemies fight back

[Mandemon]

Right now most players are either on Phact Bay or Vernen Wells, taking back those planets.

[Stalectos]

basically every planet has an hourly decay rate so if not enough divers are doing missions on a planet progress will decay to 0. if you want to see the decay rate of a planet there are websites that can show you. steam doesn't like links last I heard so I'll just encourage you to google it.