A methalox engine is fed from two cryogenic fuel tanks. Why can't the methane and oxygen be mixed as gases, in the desired proportions, and then chilled to a temp that liquefies both? From a single tank a single turbo pump could then feed this into the combustion chamber (part of flow going thru the nozzle cooling channels). Yes, a bit of same mix would be tapped off to power the turbo pump.
Saves the weight of tank bulkheads, separate plumbing, reduces turbo pump complexities. Must be a reason or the rocket scientists would already be doing this, but would like to know what it is.
Edit: Thank you to all who answered. Even the imperfect answers helped, as the comments helped me work through the whys and wherefores. I did know a methalox mixture, if it could exist, would be highly dangerous, but unsure how dangerous compared to a failure/fire of one tank causing the other tank to rupture, mixing the two. Even I can now see why the rocket scientists got it right.