There is simple chemistry behind obesity and negative outcomes from Covid-19.
Fat cells release adipokines.
One of these is adiponectin which is very protective of our body.
It reduces inflammation/suppresses inflammation. It suppresses cardiac diseases. It suppresses metabolic disorders... among a lot of other benefits.
However, when a body has more fat cells than necessary (i.e. obesity), this causes a significant decline in the release of adiponectin; called an autocrine feedback mechanism.
This in turn causes a cascade of related health issues that weaken the body's immune system and increases the potency of the virus in attacking critical organs/systems. [Drbeen Medical Lectures]

See the study by Nigro, et.al. ~
New Insight Into Adiponectin Role in Obesity and Obesity Related Diseases.