Gas clouds are made of light molecules that a plant would need a large mass to retain, perhaps. Consider how Earth's gravity isn't strong enough to retain He.

When I first read this I was wondering who He was, I guess you mean helium

But Jupiter’s gravity is strong enough to retain helium and hydrogen.

After the planet has formed, yes. You need something Jupiter mass to already exist as a dense planet to retain those gases that way though. Before that forms the gases disperse too easily so you never get to the Jupiter mass planet stage.

It's only if the mass of the cloud in it's dispersed state is significantly greater than that of Jupiter that it's gravity is strong enough to prevent it's constituents maintaining dispersal due to their own heat.

> Earth's gravity isn't strong enough to retain He.

Escape velocity is dependant on temperature, so Earth gravity can't retain He at Earths temperature - A colder Earth perhaps could.

Light molecules? You mean like, photons?

I kid

I suspect it may not be able to cool quickly enough. When a cloud collapses the gravitational potential energy goes into heat, and that heat has to be radiated for the collapse to continue. If the gas is too cold or too low in density it may not (I am guessing) be able to do this fast enough before the cloud is either disrupted or accretes too much additional gas.

“An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force.“

https://en.wikipedia.org/wiki/Star_formation#Cloud_collapse