VO2max is proportional to how easily gas is exchanged in your lungs, with whatever lung capacity you have. Then it depends on youthful but fully matured red blood cells with hemoglobin (so anemia is bad), and serum myoglobin helps too. Then, assuming your muscles are well developed, with adequate intermediate twitch muscles converted to a more slow twitch functioning, and capillarity developed to match, then the oxygen has someplace to go in aerobic running. Anaerobic development helps you run faster, but doesn't get trained much in developing velocity at VO2max. If you have adequate myoglobin for diffusion and transportion of oxygen to your mitochondria (myoglobin assists in the diffusion of oxygen), and if your mitochondria have been proliferated and enlarged, you can take in more oxygen to support more oxidative phosphorylation, and thereby produce more ATP.
So, in broad strokes, develop or improve your lungs, red blood cells and hemoglobin, capillarity, myoglobin, mitochondrial oxidative enzymes and you will have better VO2max. Just follow the oxygen, and give it more places to go.
There are times when runners work out too hard or too long and beat up their red blood cells faster than usual, and new red blood cells are instantly produced to replace them, but, until they mature, they aren't fully formed, and can't carry enough oxygen to your muscles. So, this is one part of overtraining that might take 3 or more weeks to recover from. Viral damage in your lungs can take a year or more for your lungs to fix. There are tons of ways to mess up your VO2max with illnesses and substance abuse or poor nutrition. Just don't get sick! Getting over an illness quickly doesn't mean that your running hasn't been severely impacted by it. Don't train hard when ill, it just adds to more free radical damage and loss of function.