It's a result of political division in US. If you are on the left then you have to see lab leak as a racist rightie conspiracy theory or you will have issues fitting in. Also lab leak is rejected as a side effect from being confused with intentional leak/bioweapon theory, which is entirely radioactive.

Political right is the other way around.

It is not conclusively proven one way or the other, but most people just made their conclusion: left that it's the market, right that it's the lab (or bioweapon for especially out there).